Listen to the Doc.
You are young, your brain is still growing and forming, it is the worst time to receive damage to it. Smarter fighters are better fighters, and dumb engineers well there aren't many of them.
Take 3 months off, maybe do some strength work (15 is a good age for that).
Then keep up the strength and do 9 months of grappling. Once the year is up ease back into the stand up sparring or maybe even wait longer. You can be quite a good fighter with only stand up drills (no sparring) and hard sparring in grappling. Eventually you will need to sparr if you want to compete but it can be delayed easily.
If you do that, yes your stand up may slip back a bit (but perhaps more technical) however your grappling will come along massively and at the end of that time you will likely be just as good a fighter and on the plus side you don't needlessly risk significant brain injury which would put an end to both poetential careers.
Guida, Cerrone, GSP, G-Sot, Carwin, Kampmann, BJ, Paulo, Forrest, JDS, Machida, Noke and ya gotta love Hunt.
Barao to rule them all.
Never forget the freedom fry!!!