Well, I'm not experiencing this. Every time one of you says "do ________ and you'll see it", I go do it and I don't have the same issue. I compare devices still running 8.4.1, one in one hand and one in the other doing the same stuff. Zero difference. So stop chalking it up to some not being as perceptive on "smoothness" as you are.
Only issue I'm having right now in iOS9 beta is that when you swipe down to use Spotlight Search, the search screen is superimposed over the home screen rather than the home screen disappearing. So stuff is unreadable. I've reported it in the feedback app.