after factory reset can nexus get lollipop through ota?
If your Current Rom Country (Or region) have Lollipop Update,
yes you can.
Else (Install manually) :

For find Frimware :

Where can I find stock or custom ROMs for my Android device?
Or download factory image : (developers.google)

How to Install :
( From android.stackexchange )


How to install Android 5.0 Lollipop on a Nexus 4
How to manually install Android Lollipop on a Nexus device