Updated my late 2015 iMac with Catalina now everything runs real slow

Please download and run Etrecheck  It is a diagnostic tool that's very useful to us in finding problems. Also it will give us further specs on your Mac. After it runs post the log file here. It will contain no personal information. Allowing full drive access will improve the quality of the report.

To post the log file click on share report and use the Additional Text icon in your reply window.

Just to clarify, In EtreCheck you need to click Share Report > Copy to Clipboard. Then when you click Reply > Additional Text, you need to click inside the window that opens and press "Command + V".

Probably just an unfortunate coincidence, software can't break hardware. If you want to double check the hard drive run Drive Dx, it's a much more thorough utility for checking the health of your hard drive.

https://binaryfruit.com/drivedx

Your hard drive is failing and needs to be replaced. An SSD will make a dramatic difference in speed. Make a good backup now if you don't already have one.

How to use the Add Text feature when posting your EtreCheck report

You need to copy it to the add test field or, try pasting it to the clipboard.

Why are you replying to me?

Sorry. Was aiming for the OP.

Might be time to see an Optometrist. 😎