The emulator wasn't slow before if you picked a decent x86 image. Instant run only works in the smallest kinds of cases and any amount of time saved with it is wasted by fighting it when you know it won't work...
The bigger question here is why does google spend time on toys like that rather than actually add stuff that people need? They are pushing material design - but you can't use cardview, recyclerview, and such in the UI designer and you're forced to go back to editing the UI by hand. Why do I have a UI then?
Seriously - I know this is just bitching and probably the last thing that the people who worked hard on 2.0 need but this feels like adding cupholder to a car without breaks.