I have heard the phone software re-indexes itself or adjusts to the phone, apps, space etc. So it might run fine after a week or so.My iPhone 7+ is running iOS 15 well but seems to be eating the battery faster than iOS 14. I’ve let it settle for a few days before making this assessment. I just upgraded the wife from a iPhone 6S to iPhone 13 Pro and there is no comparison between the 7 and the 13 when it comes to battery life (or anything else for that matter, other than Touch ID because of COVID). Most likely will have to upgrade my 7+ next year when the iPhone 14 comes out. Wanted to hold out until iPhone 15 but the wife’s 13 is putting my 7+ to shame and is really making me want to upgrade. Both the 6S and 7+ were purchased new when it launched and have had their batteries changed (by moi) so they’ve served us well and is a testament on how superior Apple products are compared to Android (I had a Nexus 6P and was all Android before that).
I believe that support for iOS14 will be here post iOS 15. I am curious to see if it is supported in iOS 16. I suspect it might be.
Apple are probably praying the iphone 7/8 plus's suddenly stop working as I think they are still widely used.
iTouch is so good. I hate that notch and face id.