This is worth noting. I really wish Apple would focus on the speed of interactions with the phone. Having to tap or swipe several times before it responds really messes with the flow.
It started with iOS 7.0, which is brutal. The animations wouldn't let you do anything until they were settled, and then another 1/2 second. Some people claimed they didn't notice, but 6 months later when 7.1 came out and gave back some of the speed, it was quite evident how bad 7.0 was.
Funny thing... I remember back in the day there used to be charts showing the response time of the touchscreens used in the flagship phones. Apple's were always the best, though these were measured in tens of milliseconds. Now, the phone goes unresponsive for 1000 ms at a time, and many people seem unconcerned.
I suspect that I just use the phone more quickly than most. Muscle memory lives long!
I remember buying the iPhone 5 and the thing was literally impossible to lag on iOS 6. Everything flew.
I'm the type of a person that's extremely sensitive to lag and fps drops. I have been known to drop game settings to medium or low just to have that 60 fps, and sadly iOS 9 has made my 6+ almost unusable. There's 500-1000ms delay on virtually every app launch, keyboard stutters etc. it's ridiculous that 1 year old phone could become this bad with the new OS. Feels almost as bad as some of the android 'updates'