To recall, the Samsung Galaxy S6 and Galaxy S6 Edge+ smartphones had recently started receiving the same Android December Security update. Users report (via Sammobile), the Galaxy Note 5's security update brings improvements to voice calls, apart from security enhancements. Samsung has also made it clear that downgrading after the installation of this update will not be possible. The company has also detailed its December security update on its dedicated website. It said, "Samsung Mobile is releasing a maintenance release for major flagship models as part of monthly Security Maintenance Release (SMR) process. This SMR package includes patches from Google and Samsung."
To recall, soon after the revelation of a major Android vulnerability called Stagefright, which affected large pool of devices, Google and Samsung announced plans to release security patches for its devices about once every month. This was soon followed by other Android OEMs including LG and Motorola. An earlier report had claimed that out of all the Android OEMs, LG was best at offering security updates for its devices.