Why does my App start incredibly slow (10s+) at first run, showing only white screen on android 5.0?

This is because Instant Run takes awhile to load. The blank/white screen will go away in production builds.

I'm not sure why Instant Run takes so long to load. If you look in the app's internal cache directory you will see quite a few dex files. There was an article about how Instant Run works posted a couple days ago here: https://medium.com/google-developers/instant-run-how-does-it-work-294a1633367f#.ntl30mbe2

You can disable Instant Run or just be aware that your production builds will not have this blank white screen.