iOS 26 on iPhone 15(128GB)

Was your device Jailbroken? If that's the situation, please be informed that attributing the issues to iOS updates may not be accurate.

I have been updating my devices ever since I bought my first device in 2009. iPhone 3Gs, 4S, 5, 6, SE (1st Gen), 7, 8 and iPhone 12 Pro, iPad Pro, iPhone 13, Macbook Air 2019, MacBook Pro 16"

I never had any issues with any iOS, iPadOS, or macOS updates to date.

I would personally recommend everyone update their devices instead of listening to rumors from people who may not have kept their devices free from any spurious software.

iOS / iPadOS devices cannot be hacked or infected with Virus / Malware / Spyware if it is updated to the latest iOS/iPadOS unless you have intentionally downloaded spurious software or unauthorized apps directly from the internet and installed them on your device or/and have Jailbroken. 

iOS updates generally aim to enhance user experience, boost security, and fix bugs rather than disrupt core features. Issues after updates might stem from underlying, unmentioned factors. Updates won't typically alter personal data but may refine settings or features. Backup before major updates for safety. Review Apple's update details and backup advice for a smooth process.

This seems purely coincidental, so please check the settings on your device.

See what each update does: OS — iOS 26, About iOS 18 Updates, About iOS 17 Updates, About iOS 16 Updates, About iOS 15 Updates, About iOS 14 Updates, About iOS 13 Updates, About iOS 12 Updates, and so on...

Immediately after update your phone will use more battery, feel warmer, and may notice a little lag when navigating the UI. This will continue for about 3-5 days while the files are being indexed in the background and the object detections algorithms are running on your photo library. All this is normal and documented here by Apple.

About Apple software updates - Apple Support

Mac Jim ID is correct. 💯

The only advice I can offer is to visit your local Apple Retail Store and see for yourself.

Play with it and ask questions to the trained staff.

Good luck! 👋🏼😉