Masturbation till he cums generally takes care of this problem..If it persists a little later, he should just excuse himself and go play with himself until he ejaculates again. There are just so many ejaculations during the course of a day even for a teenager.
Wed also had the same problem. We didn't mind that our son started getting erections at home all the time. My wife always sit with her legs open giving him a good view. The problem arose when he started getting erections when we went to our local nudist resort. He got embarresed to the point that he didn't want to go anymore because the other kids made fun of him. My wife just told him to come stand close behind her when he felt an erection coming on. That way no one would see it until we could get him a towel to cover up with. This seemed to cure his problem but he did spend a lot of time behind her.
I think there is nothing wrong with having an erection, being 15 years old is a natural thing, the subject brings me back to when i was 15 I use to get erections for no reasion I still get them somtimes when I am talking to a lady all I know it feals good and nice to go and relive myself in private
I know I am chiming in a little late on this topic/question. Your son is surely 16 or close to it by now. Had I seen this a year ago, I would have suggested continued exposure to nudity in non-sexual situations and let him adjust to it. When I was 15, I couldn't leave my penis alone for a full day. It's just part of being that age.
I agree with all the above comments, it's no (ahem) biggie. But here's the thing, too. Do you worry about your son seeing your erect nipples? Or your daughters? Think of it that way. It's just that the male reaction is more obvious.
And I hope your nudist friends would see it the same way. What a thrill and confidence booster for a young guy if a woman your age or older were to come in, see his hardon and after greeting him say something like. "Beautiful cock!" And maybe give it a little squeeze. Then the conversation moves on.
I think it is unnatural to need to masturbate to get rid of the chance of a public erection. What is more natural than an erect penis? I think those who are concerned with it are control freaks. I enjoy erections, I like to look at them, and I know others look at mine.
Boys & their "toys" will be randy whenever there is stimulation. I still get "IT" at nude beaches & resorts. I have learned to JO B4 going outside. But, it still happens, depending on the scenery. Seeing other nudists just makes me think of a total "group-grope". All in, all the time. Nudity is fun and should be enjoyed as a Naturist/Nudist. Not a sexual thing. He will be fine as long as you and others let him know everything is "natural; not dirty.
Of course he's going to be erect a lot of the time.
Those suggesting you, or his sister, 'relieve' him obviously aren't thinking about the fact that he'll expect it next time too, and the time after, and so on.
And, to be honest, at his age he'll be hard again 10 minutes later anyway (if he softens at all.)
Naturists expect it of boys from puberty until they learn to control it, 99% won't care providing he doesn't make a big thing (pun intended) of it himself.
When I started to go to nudist beaches (and camps) with my schoolfriend and his dad we boys were encouraged to masturbate before we left the car, in an attempt to keep us soft in public. It worked for minutes, and to be honest nobody cared that we were stiff anyway.
Now I would suggest buying him a tablet, get him playing some game that takes his mind off his erection, sit back and enjoy the sun without worrying about him.
That is great, good for him, shows that he has the ability to make it stand at attention. Being that age is of course going to bring him to an errection almost all the time. Don't put him down, rather encourage him to express himself, which it sounds like he is certainly doing. It is great that your able to share the experience and he is ok with showing it off. Heck, if someone doesn't like to see it, they can always close their eyes ! Always nice to see a tool doing what it is suppose to do, awesome I say !! :)