First, why do you need to tell them why you're not able to make it? They didn't consider anyone else by letting their 15 yr old unlicensed kid come!
Second, think about this the 15yr old WILL be a distraction for you & everyone else on the ride. I wouldn't want to be worrying about him so much that now I'm not truly paying attention to whats going on around me.
I'm sure he has a good ability to ride because I cant imagine parents putting their child in that situation. Still I don't think it's a wise move. It's your call.
Second, think about this the 15yr old WILL be a distraction for you & everyone else on the ride. I wouldn't want to be worrying about him so much that now I'm not truly paying attention to whats going on around me.
I'm sure he has a good ability to ride because I cant imagine parents putting their child in that situation. Still I don't think it's a wise move. It's your call.