On Xda there is a full system dump of 6.0 for the Tmo N5. A user had an IMEI problem odin back to stock fw and low and behold he had a system update to non other then 6.0. Now the waiting game for the devs to do something with that.
Samsung confirmed (or leaked, can't remember) that the Note 5 and S6+ Edge should see Marshmallow for the International versions before the year ends; leak claims December ETA.
So after that it's up to the carriers to do their tinkering.