Samsung has released software Update N910FXXS1DQC3 for Galaxy Note 4. The new update includes Android March Security patch.
Android March security patch includes fixes for vulnerabilities and exposures in the Android OS. The update also brings stability improvements, bug fixes and further improvements for performance.
Software Update N910FXXS1DQC3 for Galaxy Note 4 will gradually roll out to everyone. However, you can also check manually for updates, Go to Settings > About device > System update.