I remember 15. It was 1977 - 1978, which I am sure feels as ancient as when the pyramids were built.
This angst is, it happens to a lot of people. A few things that helped me -
* Getting exercise of some sort, e. g. get out of the house, go for a walk, etc. If that's not in the cards, do you have a bike you could ride? An intramural program at school? It does not have to be organized sports. Dance is fine, even if it's just in your room, to your music. Walk the dog. Just, move, in whatever way works best for you.
* Making art. It does not have to be good. Just, make something. Write a story or a poem. Paint a picture. Draw. Knit or sew if you like crafts.
* Building something. Make a model rocket. Build with Legos. Put together knocked-down furniture. Whatever floats your boat.
* Not being alone. Call your friends, or text them. Go to a friend's, or have them come to you, or go to the movies or the like. There are a lot more options for contact than there were back in the Stone Age.
As Set said, this, too, shall pass. Really.