Meeting your soul mate at that age is extremely rare. What is most likely is you have met the person who is your "first love". It is a strong connection and one that is cherished throughout your life. But it is not soul mate worthy. At 15 you still have a lot of growing up yet to do.
I say this all with the presumption that this person is within a year or two of your age. If they are older than that then they can be manipulating you, or it maybe a one sided relationship.