The Android 5.1 Lollipop made the phone smoother, more secure and added HDVoice capabilities between two compatible handsets powered by Android 5.1. This update carries a build version of LMY47D. The Nexus 6 received an Android 5.1 Factory Image listing that was slightly different than the version of Android 5.1 that arrived OTA.
The Android 5.1 build that is used for the Nexus 6 Factory Image has a build version of LMY47E. What is different between this and the LMY47D build that was sent out OTA? The version of Android 5.1 used for the Factory Image contains an update to the radio image. This controls different signals like Wi-Fi, cellular network connectivity and Bluetooth. Will Android 5.1 version LMY47E be sent out OTA as an update to Nexus 6 users? If the change is no big deal, it could be left up to the owner of the stock Android phablet to flash it on his handset if so desired.
The Factory Image is used to flash the latest stock Android build on a Nexus device. It could be used on a device to make sure that a rooted handset will receive the next OTA update, or when a phone owner finds that his customization plans have gone terribly awry. If you need to flash the Android 5.1 Factory Image to your Nexus 6, click on the source link below.