iOS 9 was created to improve performance partly.So yes performance is a VERY big part of each update as its one of the headline feature
"Performance" is subjective once again. It's not a bug or change that can be quantified. All of the tiems in the OP are quantifiable bugs or changes. The lag argument should start another thread as not everyone even sees it.
In fact well over 50% of people in the poll here say 9.2 is faster for them over 9.1, 38-21 (idk what the bottom choice is for frankly). If it wasn't subjective then everyone would be seeing it.
Idk why you're so gung ho about this lag crap and have such a huge objection to starting it's own thread. Doesnt hurt you one bit and lets us actually discuss the beta itself- the point of this thread.