in most places it is illegal for a girl to get married at 15, so that would probably never happen unless she got permission from the courts to get married at 15, which normally they only give is she is pregnant. and if that were the case, chances are her parents are not going to be giving her a quinceanera.
ok is the person is 15 nd getting married. 15 is a very special occasion. Wait till the person is 16 atleast. You will regret having both together. They arE both the most special occasion on a girls life. Dont ruin it.
Change the dates. I know its alot of money but each celebration indicates different things. one is you arent a little girl anymore and the other is that you are now a woman moving on with the love of your life. VERY DIFFERENT.