the 7 on 7 is the least important part of the camp, I wouldn't get to worked up about it.
If your concern is being noticed, you should be focused on the position drills and the 1 on 1's and which group your son is in and if he gets bumped up to the next group up. That is where the vast majority of the evaluations are happening. Realistically at 15, he isn't going to be in one of the top groups unless he is worthy of an offer right now, if he needs to develop, then realize that and let him develop this year, 15 is still young. The position coaches typically aren't involved in the 7 on 7, but yes, they are competitive, as the counselors and the kids want to win the tournament (my son won the tournament one year, I think they get a tshirt for it, it had very little impact on his evaluations in my opinion)
Also not directly related, but if you are looking for a great receiver camp, I would highly suggest the receiver tech camps put on by the Collies, one of the best camps that really improve receiver technique, I highly recommend them.