Although there is no precise date, we now know that T-Mobile has approved the Nougat update and the rollout of the new firmware should begin by the end of this week. There are no details about the changes, either, but we do not expect any surprises.
https://www.notebookcheck.net/T-Mobile-Galaxy-S6-and-S6-Edge-to-get-Nougat-this-week.226152.0.html