Note 5 system dump with Android 6.0 Marshmallow appears, hints at an imminent update
Granted, the user that got it had a bit of unusual situation with lost IMEI, and rollback from a custom ROM, thus fooling the system to release it prematurely, but the fact that it is ready and, seemingly, fully functional, only hints that an official rollout is not far away.
The user said there aren't too many visual changes, but they've been asked to give permissions for every action (that's one of the new features in Marshmallow), plus there are some differences in graphical details and layout. The build number of the Android 6.0 Marshmallow for Note 5 is Android 6.0 Marshmallow is MRA58K.N920TUVU2DOK5, so that's what you should be looking forward to in the next few weeks if you have a Note 5.
source: danon.brown (XDA-Devs)