Honestly, I coped by sending him off to things before the age of 15. But in your case, that's kind of like closing the barn door after the horse has escaped. So I get that this is really, really hard for you.
Let me help you (I hope) by saying that this trip is more than fun for him. This is absolutely vital for him to develop skills he's kind of behind in learning! You spelled them out - independence, confidence and self reliance. That means you have to resist (and I mean RESIST) the urge to text all the time! Accept that, if there were bad news, you would absolutely hear right away. So no news means he's engaged, involved, happy and learning!
A 15 year old who has never been away for more than a week absolutely needs to jump in with both feet before he's an 18 year old going away to college for months and months!
What I would do, if you are financially able, is get a life coach to help you figure out what else you are and want to be, besides a MOM! I know you don't want to be the person who has an anxiety attack at college freshman orientation when the dean says, "Look, your job is DONE. Don't call the professors to ask for an extension, don't call the health services department to find out if your kid had treatment for strep throat or a consultation on sexual activity/contraception/STDs, don't call the RA to find out if your kid is getting along with his roommate. You're getting the bills, and nothing else." (And yes, I heard this at my son's orientation, said with loving firmness at an excellent college with a great residential life program.)
I'd work with the coach to find out what other areas you are "helicopter-y" in. Are you doing your child's laundry? Stop. Teach him. Require him to do it. Are you nagging him about eating vegetables? Stop. Put the food in the fridge and let the boy get sick or fatigued if he's determined to.
Have you seen the articles from business leaders and HR managers who are fielding calls from helicopter parents of 24 and 25 year olds, saying that Jimmy needs a raise or Susie needs a more supportive supervisor? If only those parents had practiced more distant parenting when the kids were 12 and 15 and 18! So start now, and get a jump on those days to come.
I think it's like quitting smoking or giving up caffeine or ripping the bandaid off. It's gonna hurt like hell in the first few moments...or weeks...but then it will get easier! You want to become the parent who can happily and confidently say, "I have no idea what my kid is doing at this exact moment, but I trust that he is fine and making good decisions. I trust the job I did as a 'mentor' and 'training supervisor' and now he's got to make it on his own and make some mistakes." Breathe, get a coach, have a shoulder to lean on, and you will get through it. Yes, yoga and meditation and all those things can help, but only if you are secure in your thinking. I'm not sure you are there yet - so work with someone who knows why you are feeling what you feel, and who helps you get the right mindset before you get to yoga class!