Although my (1st gen) initially didnt like 5.0.0, then I cleared cache and tweaked settings and it improved, it has been slowly degrading since.
So I have just rolled it back to 4.4.4 which was stable and slick.
However, I was using Wug Fresh Nexus 7 root tool kit and somehow got within a gnat’s tadger of bricking the N7. Just about managed to fluke a rom flash. I was going to recommend it as a route back to safe running, as Ive done rooting before (and even used the Wug Fresh toolkit as well before) but even though Im not an XDA god myself, I cant now recommend to anyone who doesnt have oodles of confidence to have a crack at it given how lucky I was not to brick it.
I may have been unlucky, but I got stuck with a locked bootloader and only just managed to unlock it. Others may be able to do the roll back safely enough.
If you want go, start with the You Tube video: https://www.youtube.com/watch?v=5JXGLNnSzGQ
but you’re on your own.
At least mine is back to top notch performance and ready for Stoner Jr to minecraft his butt off.