Damn how I wish I had read your post before! I received this update last week, yes, on January 2015, and happily (and stupidly) updated Android, thinking "yes, 'til now, all updates have been improving my Nexus 7 performance and look & feel.
Wrooooooong! Lag after lag, it's becoming almost impossible to use my Nexus 7. Now it's as slow as the worst Android tablet in the market. On top of that, several apps crash, like FireFox, FireFox beta, Dolphin Browser, etc. Even Chrome and Facebook crash after some minutes of usage.
Plus, after I reboot the tablet (it even takes longer to boot than when I had KitKat) it still keeps in memory all the apps you were using, so... when the heck does the memory clean itself??? I mean, this seems Lollipop is not "flushing" the cache as it was supposed to after rebooting.
How I wish I could switch back to KitKat, but without rooting AND without losing my personal information.
I mean, I can backup my pictures and contacts but... what about the progress in my games? I would have to start each game over again and get to the current levels.
Seriously, why would they release such a slow, unefficient and crappy looking operating system? Android was great as it was, no such improvements were needed. Damn! Take it back to what it was! I hate when I slice down the LEFT menu or the RIGHT menu and BOTH menus show at the screen CENTER! Why would anybody want to mix up alerts with system configuration menus???
I hate Lollipop. I doubt the next Android version is like KitKat.
I'm seriously thinking of ditching my Nexus 7 and get an iPad.
P.S.: I even tried a fix called "wipe cache partition" which you can google to find the link (I'm a newbie here and can't post links) and it worked fine for some minutes, but then it started lagging again. I think that fix is quite fine, but there are also other issues that have to be addressed in order to get the good ol' performance back again.