My 15 year old girls has asymmetric breasts. Will this self correct with age?

Probably not. Few are truly symmetric. The norm in human beings is that one side is slightly different from the other, not just breasts, but all over; like one ear a little higher or one arm a tiny bit shorter. If, when she is mature, the asymmetry bothers her, it can be fixed surgically (i have known several who have done this with good results).