
Do you mean 16 weeks? It is not unusual in prick eared dogs for the ears to go up at very variable ages! If they are not really firm before a puppy gets into teething, then they wil often flop down again, and also sometimes beup in morning and down later in the day.
Chewing will help the teeth and the muscles in the jaw and ear base.
If he is 15 months, then I doubt very mush his ears will ever be fully erect!