I kept my Galaxy S5 as a backup device in case I have problems with my S7. I periodically plug in in to charge. Today I decided to plug into the computer and run Smart Switch on the PC to check for updates. To my surprise, there was an update to Android 6.0.1 Marshmallow waiting.
Looks like T-Mobile has stopped using updates as a tool to force people to buy new devices. I like the trend. :)