NBA 2K16 Demo Release Date
If we see a NBA 2K16 demo release date the most likely timeframe would be the middle of September 2015, about two weeks before the release date.
You shouldn't hold your breath for a NBA 2K16 demo this year. For the last two years 2K Games did not offer a demo of the game and there is not a major need to offer a multiplayer beta like with Call of Duty game.
We could see a change, but unless you hear a specific announcement from 2K Games, do not expect to see a NBA 2K 16 demo release this year.