The WiFi Calling update for Nexus 6s running on T-Mobile that began rolling out over the weekend now has a factory image and OTA .zip file from Google as build LYZ28E. This is still Android 5.1.1, of course, but the files may come in handy for those of you running your Nexus 6 on the Uncarrier’s network and have yet to receive the update.
You can download the factory image here. Instructions for flashing factory images can be found here.
Update: Google also just posted the 5.1.0 “LMY47M” (T-Mobile Only) factory image. You can grab it here.
If you need the OTA .zip file, you can grab that here (LYZ28E from LMY47M, 126MB). For instructions to sideload using adb, check here.