According to tipster @mmddj_china who is based out of China, Samsung has started testing the Nougat update on multiple Galaxy C series devices. Specifically, Android 7.0 is being tested on the Galaxy C5, Galaxy C7, and the C9 Pro.
He also notes that it is the Chinese variants of these phones. There is, however, no information on exactly when the roll out will begin. Given Samsung’s track record, it may take sometime before the update arrives officially.