Sure they have. Not sure if anything like that would get called out in a beta update, but things of that nature have been called out by Apple in public releases.
In that case, technically, iOS 8.2 didn't bring any performance improvements. Which I guess on the one hand might be difficult to quantify if you for instance remove excess code which makes the UI run a bit better.
Anyway, I find myself seeing that maybe auto-scrolling has improved somewhat with 8.2 in terms of not stuttering as much. It's still not consistent or good enough though.