I think I've found my soulmate, but I'm only 15?

There's a very small chance that he's your soulmate. But it sounds like your first love. I know because mine went exactly like that :) And I will never forget him, and will always love him. You're at the age where this is bound to happen. Enjoy it while it lasts, don't think about it too much. Because if you lose it, you'll always wish you could have that feeling back. But you're young, so like I said, just enjoy it :) No need to overthink