hello vikramaditya singh,
as you got 15500 rank in the reservation category it will be some tougher you to get seat in the best NIT according to your rank .and also the aerospace will be course in some colleges only .so the seats for the aerospace will be short so you it will be the toughest competition during counselling complile with all colleges offering aerospace course and wait till the last round and spot round to get a better college

Hello

With that rank and on the top being OBC will definitely give you a seat at a good college offering Aerospace engg.

Best of luck!!!