For what it's worth, my friend Patrick Collison wrote an aware winning Lisp at 15 -- and is still hacking.
At 15 I never brought it further than writing small basic programs on a tandy 'pocket' computer.
The first time dabbling in languages was writing a 6809 macro assemlber, but that had to wait until I was 17. Those really young kids cranking out code at that level really amaze me, I don't think I had even heard of LISP at that age.
Patrick Collison is really impressive, and I had the fortunate chance to randomly meet him at a coffee shop (he probably doesn't remember me). He is a YC alum, having founded and sold Auctomatic. He later created and sold an iPhone app that was a locally compressed copy of Wikipedia. Very cool. http://collison.ie/
I wrote a bit about how I ended up getting into Lisp at http://lemonodor.com/archives/001038.html. (And I'm glad I did, because I can hardly remember now.)
Not just because of your age, but mostly because you have things so 'together' at your age.
Most kids at the age of 15 are laying the seeds for the wasting of the next decade of their lives, you decided to lay the foundation for the rest of your life instead.
Keep going! And don't burn out! (please) The energy pit is not endless, even if it seems to be so. I've found that out the hard way.