Can an external SSD speed up my Vintage 2015 iMac performance

Yes you could benefit with an external SSD to boot and run from. Get one that is compatible with Thunderbolt 2.

However, before you do consider this, as you've already been told, there is no reason to ever install or run any 3rd party "cleaning", "optimizing", "speed-up", anti-virus, VPN or security apps on your Mac.  This documents describe what you need to know and do in order to protect your Mac: Effective defenses against malware and other threats - Apple Community and Recognize and avoid phishing messages, phony support calls, and other scams - Apple Support.  

There are no known viruses, i.e. self propagating, for Macs.  There are, however, adware and malware which require the user to install although unwittingly most of the time thru sneaky links, etc.   

AntiVirus developers try to group all types as viruses into their ad campaigns of fear.  They do a poor job of the detecting and isolating the adware and malware.  Since there are no viruses these apps use up a lot of system resources searching for what is non-existent and adversely affect system and app performance.

There is one app, Malwarebytes, which was developed by a long time contributor to these forums and a highly respected member of the computer security community, that is designed solely to seek out adware and known malware and remove it.  The free version is more than adequate for most users.  

Unless you're using a true VPN tunnel, such as between you and your employer's, school's or bank's servers, they provide false security from a privacy standpoint.  Read these two articles: Public VPN's are anything but private and Security Risks: The Dangers of Using Free VPNs (eccu.edu).

So uninstall Trusteer and AVGAntivirus according to the developers' instructions. You can check to see if you've removed all of the supporting files by downloading and running the shareware app Find Any File to search for any files with the application's or the developer's name in the file name.  For the two items methtioned you'd do the following search(es): 

1 - Name contains trusteer

2 - Name contains avgantivirus

Any files that are found can be dragged from the search results window to the Desktop or Trash bin in the Dock for deletion.

FAF can search areas that Spotlight can't like invisible folders, system folders and packages.  

If you get warnings that the file can't be deleted because it is in use or used by another app boot into Safe Mode according to How to use safe mode on your Mac and delete from there.

Note:  if you have a wireless keyboard with rechargeable batteries connect it with its charging cable before booting into Safe Mode.  This makes it act as a wired keyboard as will assure a successful boot into Safe Mode.

Well done on uninstalling Trusteeer and AVG, that is an improvement. However your DriveDX report only shows part of your drive. Let me explain, your computer has a Fusion Drive installed, a Fusion Drive is a traditional spinning HD fused with software to a small SSD. The report you posted shows the drive HOWEVER it does NOT show the spinning HD which is the drive we suspect may be failing. You need to dig into the report a bit more to locate the spinning HD, that is the 2nd Macintosh HD on the left pane. So select that drive then look at the report on the right side. If ANY errors appear that indicates the HD is failing and you should really replace the computer.

However if the report shows that drive as okay then it is possible you have a split Fusion Drive, meaning the software fuse has become undone and needs to be refused. Before we go down that path, lets determine how the spinning HD's health is.

Your second drive repor from EtreCheck:

Performance:

System Load: 2.92 (1 min ago) 3.26 (5 min ago) 2.56 (15 min ago)

Nominal I/O usage: 7.79 MB/s

File system: 19.74 seconds

Write speed: 343 MB/s

Read speed: 810 MB/s

show your Fusion Drive is probably healthy ( File System = 19 seconds) BUT is still moving data far below expected speeds. Your nominal drive speeds on that iMac model should be Writes between 600 and 900MB/sec and Reads over 1300-1400MB/sec.

At this point an external USB 3 SATA6 SSD would increase your Writes to about 400MB/sec BUT would reduce your current Reads to the same value. So, to your original SSD question, not at this point.

Did you restart the computer after removing the dreckware?

👉🏻Etrecheck does not show your Fusion drive as "split," but there is a simple test in the "Before You Begin.." paragraph of this Apple article:

How to fix a split Fusion Drive - Apple Support

is easy enough to verify your Fusion's condition:

Processes starting with "md" are related to Spotlight indexing. The are very active right after a restart, so may not be applicable to your issue. You can reduce how many thing Spotlight indexes:

Spotlight settings on Mac - Apple Support

Example: if Spotlight is indexing slow USB external drives, that can slow overall performance

I would try disconnecting your external drives and doing another Etrecheck test to compare the internal drive speeds. I have seen a few cases where WD Passport USB drives are slowing main drive performance. Testing without the external would at minimum eliminate them as suspects.

You have only 8GB RAM in this iMac and you're running macOS Monterey & Google Chrome. That would be a root cause of poor performance. You can add another 16GB for only about $30, for a total of 24 GB RAM. It would make a difference.

Also, your Fusion drive read/write performance is not great although there is no information in your Etrecheck or DriveDX reports that explain why that is so. My guess is that APFS is the culprit; it has always been known to be unkind to performance on Fusion drives & traditional HDDs. Unfortunately it is the required disk format for all versions of macOS Catalina & later. An external startup SSD connected via one of the Thunderbolt ports would significantly improve performance.

I suggest getting rid of Chrome, it is a known resource hog. Use Firefox instead.

Also, you appear to be using IBM Trusteer Rapport, which is yet another a/v app that should be removed unless your bank or financial institution actually requires it.

Fusion Drives originally included 128 GB of flash (SSD) space.

Apple later cut the amount of flash (SSD) space included with 1 TB Fusion Drives to a miserly 24 – 32 GB. While it is prime real estate, there is not nearly enough of it. Your Fusion Drive has only 24 GB of SSD space, and so you might benefit from getting an external SSD and making it your startup drive.

Hi there!

+1 to rkaufmann87 to remove the AVG and Trusteer antivirus software. Most third-party antivirus utilities can cause poor performance and software issues.

If after removing the antivirus software, your Mac is still running slowly, run DriveDx and check the health of your Fusion Drive. Let us know what it reports. Uploading a screenshot or the full-text report might also be useful.

-Jack

The primary problem I see is:

Antivirus software: Apple, AVG, and Trusteer

Mac OS does not require or benefit in ANY WAY by installing the following types of third party apps:

• Antivirus
• Cleaning
• Security
• VPN
• Maintenance

Your computer has 2 of the absolute worst that you could install and is very likely at least a partial cause of your slow Mac. What these apps do is the exact opposite of what users want. They make Mac OS slow, appear buggy, created unwanted behaviors and in exchange do absolutely nothing that Mac OS doesn't already do!!! In short, there is ZERO reason to have them installed.

In addition, your computer is 11 years old now and should have been upgraded a few years ago. You mention that you want to keep it in order to keep a 27" display. Well, simply get a new M4 based iMac with the same amount of storage and a 27" display and you will have a new system that FAR outperforms your antiquated 2015 iMac. A new MM with 1TB of storage is $999 and a high quality 27" display is about $300 so for less than you spent on your original iMac you have a solution. You can use the old iMac's keyboard and mouse too. In addition you then have a new 1 year warranty, are eligible for AppleCare coverage and will have a rocket compared to an ailing VW.

I agree the internal HD appears to be okay (I am kind of surprised). To check if the Fusion Drive has split please do the following:

In Finder's sidebar please check "If two physical internal drives are shown, then you have a split Fusion Drive, because you should be seeing an item on the left pane of Disk Utility called ``Fusion Drive''. "

ab137 wrote:

MartinR . Thank you. I have removed Trusteer completely (I think). Is Safari OK if I get rid of Chrome? Or is FireFox better? Will consider adding more RAM.

Safari is fine although because you are on Monterey, which is no longer supported, you will not get any more Safari updates. Safari 17.6 (July 2024) was the final release on Monterey.

Firefox is continuously updated and in my opinion has overall better privacy, security and performance than older versions of Safari.