I have struggled with the Lollipop update on my 2012 Nexus 7 for ages, sluggish performance overall and I was mainly using it as a glorified ebook reader. Over the last two weeks after a few updated Google apps it seemed to get a lot faster opening up apps and in general responsiveness but this morning there was a new update signalled, Lollipop 5.1. It just finished installing and I'll have a poke around now but the first signs are extremely positive and it seems to have regained the early days snap.