AT&T Galaxy Note 5 is receiving the update as build number N920AUCS4EQG1 while the S6 Edge Plus on AT&T network is getting the update as build number G928AUCS4EQG1. Other than the monthly security patch, the update also tags along regular bug fixes and system enhancements.
Although a small one weighing at only 22MB, the update is highly recommended as it enhances the security of your device. As is the case with OTA updates, it may take a while to appear on your device. Alternately, you can also check for yourself by heading to Settings > About device > System updates.
However, before hitting the download button charge your handset fully and connect it to a WiFi network to ensure seamless installation of the firmware update.