jbm2, you received a few responses in a different CARRIE thread topic, but I will answer here as the show you're asking about is related specifically to the LA "immersive" version. I do not recall a lot of bad language, but I would guess most 15-year-olds would not have a problem with the language even if there was a bit more of it than I remember.
In the La Mirada version, there was one brief (sorta) sex scene where you see two of the students start to undress, kiss while laying down, and then get dressed - having never gotten fully undressed. This happened way up on a platform and was not on the stage floor - and could easily have been missed. In the other CARRIE thread, someone mentioned this scene (or maybe one like it?) was between Chris and Tommy, but the scene I'm referring to was with Sue and her boyfriend and is the only scene of this type I recall.
Also, the character Carrie undresses completely during the shower scene, and that scene was not a "blink and you might miss it" moment in La Mirada. However there is a note in the LA production that there is only brief nudity, so I would guess they are toning the shower scene down a bit. If this is of concern, you might wait for early reviews.
Everything else is pretty tame, and the show is a lot of fun. The special effects and destruction scene were pretty thrilling, and I would say most relatively mature 15-year-olds would enjoy the show as a whole and not be damaged by it. My .02 cents.