Hi there!
As u probably know, the main intention of waiting till 18 yrs for orthognatic (jaw) surgery is that the growth should not express afterwards (which would mean relapse).
It's possible that ur facial growth is already complete at 15 yrs.
One of the proven ways to find out is to evaluate a hand-wrist radiograph.
Next Steps
Hand-wrist radiograph and orthognatic-Orth odontic consultation
Health Tips
In most cases u do need to put on braces for some duration so as to get a good occlusion after surgery. So just be open to the possibility.