Well one of the reasons why Nexus 7 2012 start to get slower for some people has to do with the memory technology used in the tablet at the time.
Once the tablet is filled with stuff, even after you remove it the seems to bog down significantly. And this affects the small memory variants more than the larger ones.
TRIM support properly enabled in Android 4.3(or 4.4) alleviated some of the performance issues related to memory but software can only go so far...
Android 5.0 brought along with it some of it's own issues, mainly related to memory management. I've noticed some massive slow downs on my Nexus 5 when the system was desperate for memory.
Luckily Android 5.0.1 seems to have resolved those issues for me and is running extremely smoothly.
What I would recommend doing in going into settings > developer options > process stats.
If your results look anything like this, I am pretty sure it is an Android 5.0 issue and the only that could temporarily fix it would be a reboot.
If your results are perfectly normal and you are still experiencing issues with performance a hard reset may be recommended.
In any case wait for Android 5.0.1, it fixes a lot of bugs.