Can I get 50/50 custody and have my child support decreased?

My son is 15 years old and he’s been in his mother’s primary custody since we split up. However, he goes back and forth between my house and his mother’s. He spends overnights with me, eat meals at my house, and I buy him whatever he needs for school and sports. His mother is now taking me back for more child support because she heard I got a promotion at work. The new position does not pay me substantially more money, I just get more vacation and other perks. Can I counter-sue her for 50/50 custody and have my support lessened? This makes sense since my son is with me a lot anyway and I pay out of pocket for many of his things. If I do take her back to court for custody, will my son have any say in where he wants to live because he’s 15?