The T-Mobile Galaxy Note 4 and Note Edge are receiving OTA updates with latest security patches. While the Note 4 is receiving April security patch, the T-Mobile Note Edge is receiving the May security patch.
The updates are arriving as build N915TUVS2DQE2 for the Note Edge and your device needs to be on version N915TUVU2DQC1 to get this update. As for the Galaxy Note 4, the update is identified by build N910TUVS2EQE2 or N910T3UVS3EQE2 and your device needs to be running on either N910TUVU2EQC1 or N910T3UVU3EQC1 build to get the update.
Both updates include a host of fixes and system stability enhancements in addition to the security patches. The security patch, on the other hand, deals with various vulnerabilities and flaws in the system that could be misused by hackers and the like.
If the update hasn’t arrived to your device yet, you can try checking manually in Settings » About » Software update.
Once you receive the update notification, ensure that your data and other personal files are backed up safely on your PC in case the installation fails. Also ensure that your device has at least 50% charge and download over WiFi in order to save on extra mobile data charges.