For context this was the first iPhone I have ever bought, it worked seamless : smooth, fast, no overheating and lag free.
Ever since I updated to iOS 17 I have been noticing weird lags, everything kinda feels like it has some sort of delay: typing, opening apps, locking the screen etc. Plus I have been noticing that my phone is getting hotter more usual than before when using apps such as Google Maps navigation or Spotify with my car connected to Bluetooth.
I joined the Apple camp expecting that everything “just works”, sadly it feels like an Android experience all over again, only with a greater price markup.
Apple mobile devices always experience a temporary drop in performance immediately after an OS update/upgrade while the operating system rebuilds caches and indexes, and downloads and installs app updates. Naturally, while the device is busy doing this, battery performance will also be impacted. This typically lasts from an hour or two to a day or two depending on the age and speed of the device and network bandwidth, after which performance returns to normal. The overwhelming majority of posts I see online complaining about iOS devices supposedly being slowed down or batteries draining abnormally fast by iOS updates are in this category.
Whenever Apple releases a major upgrade for older iOS devices, major new features and functionality are included, which means the device can do more things than it could before. And whether it’s a major upgrade or just an update, known security vulnerabilities are patched. Naturally new features come with a cost, and that cost is generally that the device must work a little harder to do the extra work. However, at the same time, Apple is always refining features to make devices work more efficiently.
For instance iOS 12 has been shown to be significantly faster than iOS 11 on the same device - even on very old devices:
https://youtu.be/Ius4c3pyd2M
And iOS 13 was even faster than iOS 12:
https://youtu.be/LPXDKSzv0NY
The same applied to iOS 15:
https://www.macworld.co.uk/news/will-ios-15-slow-down-iphone-3808590/
The same goes for iOS 16:
https://m.youtube.com/watch?v=UC5l0EJheD0&t=118s
And so on…
Typically, you can expect a major iOS upgrade to slow some operations down just a little bit, but also speed up some operations as well as add many new features you didn’t have before. On really old devices that are near end of life, the speed decreases may be more noticeable than on newer devices. But in general it all works out to a net benefit in real world use.