Possibly coincidentally, I’ve had touch response issues on my iPhone 6s forever. As I never updated past iOS 12.x, it’s not iOS 15 related.
I assumed it was because of 3DTouch being present (the phone not handling a tap as a normal touch; I assumed this was a design fail, and one reason Apple abandoned pressure sensitivity in later models).
I also notice it’s most likely to happen in Safari, and assumed it had more to do with website design (links will show they’ve been tapped by changing color or underlining, but Safari doesn’t actually go anywhere).
What I’ve also noticed is that the keyboard is obviously multithreaded: autocorrect, spelling, button responses, etc., are all on their own threads, because when the input is slowed down by CPU throttling or certain websites (like this one, Facebook, and twitter), the behavior of the keyboard is WAY worse.
On twitter, for example, the performance is REALLY SLUDGY. I will get completely different words, sometimes even two words inserted at a time, while trying to type something entirely unrelated to those words.
It seems that, when there’s lots of lag, the threads aren’t all “on the same page” and the typing behaviors become really bad.
It did not used to be like this. I haven’t changed the OS on this device in years because of breaking the Apple ecosystem with my Macs. Yet, keyboard behavior has been getting worse every year (including not even responding to typing at all for up to several seconds when switching apps).
Then there’s the unresponsive “Reader Mode” button in Safari’s URL bar (when it bothers to even show up at all). Sometimes three or four taps are needed before it responds. I assume that is also lag.
Once again, it seems that the bloating of website scripting will push me to a newer phone, forcing me to break compatibility with my Macs (which I’ve been waiting to replace because I can spend only once and Apple haven’t released a power-user’s desktop machine at a sane price).
It’s all the more irritating to see that Apple have still not done anything about their habit of adding more bugs and not fixing existing bugs in their Wall Street obsession with pushing more “features” to sell another bunch of new phones every year...
iPhone/iOS was never perfect, but it was never this consistently bad before 2013. iOS 7 was the end of good design and reliability.