This I don't agree with. After a few minutes my 6+ works normally. What the heck would take days to cache?
It doesn't cache the animation until you've run it for the first time, so if I reboot my device and go a couple days without using photos.app for example, the animations that photos.app uses, won't be cached yet. Why is that hard to understand?
Do you think I wanna reboot my device and go through every animation to make sure they're all cached?
I think the problem here is, iOS 8 loaded the animation into memory before it started (causing a slight delay when you tapped something, but the animation would play smoothly after) whereas iOS 9 tries to play the animation while it's loading it into the ram causing a hiccup because it can't do both things at the same time efficiently.