Google started pushing out the Android 5.1 version of Lollipop to the Nexus 7 2013 LTE model. They also made the Factory Image available to both the Nexus 7 2013 and the Nexus 7 2013 LTE.
The main difference between this and the previous Android 5.0.2 (LRX22G) version is simply a number of bug fixes. Of course, that's a pretty important thing, so it is probably worth it for most folks.
Source: Factory Images for Nexus Devices - Nexus Files for Developers Google Developers