I have installed Android 5.0 on my Nexus 7 (2012, wi-fi) and that was the biggest mistake I have ever done with my tablet pc. I don't know, maybe the problem is not in Android Lollipop, but in my concrete device, but after installing 5.0 it becomes incredibly slow! First 5 minutes after restart it works fine, but then everything become soooo sloooow....
Here are some steps that can help you with downgrading your Nexus device (5 or 7) from 5.0 to 4.4 (or whatever you want).
- Download factory image for your device from the official source: https://developers.google.com/android/nexus/images
- Extract image ( you can use 7zip to extract *.tgz files)
- Download and install ADB, Fastboot and drivers (install system wide). Download from here: http://forum.xda-developers.com/showthread.php?p=48915118
- Connect your Nexus device to the computer with USB cable
- Turn off your device
- Boot your Nexus to bootloader mode by using the key combination mentioned below.Nexus 5: Press and hold Volume Up + Volume Down + Power buttons until you see bootloader menu
Nexus 7: Press and hold Volume Down + Power buttons until you see bootloader menu
- On your computer open terminal (win+r -> cmd.exe -> enter) and go to the folder extracted in the second step (this folder should contain flash-all.sh file)
- Run flash-all.sh command in terminal
- Now you can lock your device by executing fastboot oem lock in terminal.
If your system cannot find fastboot or other utilities just make sure that you have installed ADB, Fastboot and drivers system-wide. If this doesn't help try to add path to the adb utilities to the PATH enviroment variable.
P.S. While writing this how-to I have downgraded my device from 5.0 to 4.4 and now it is super fast! No glitches, no freezes, working like a charm!