I was looking for solution on this either, stupid sumsung removed one of the best nougat control over notifications that you could define levels of notifications control and their priorities even of the list (The power controls notifications
Now or you only have 2 options:
NO PEEK+NO VIBRATION/SOUND
PEEK + VIBRATIONS
instead of the great different levels of notifications control. Samsung always does some **** to piss off users.... because they decreasing the control that the user have over the phone instead of increasing.