That will allow you to motion for change of CS or custody of that child. He will not sign suspension of CS payments as there is still a child living with him, correct?.
You may want to contact legal aid in your area to see if you qualify. You do not need an attorney to file a motion, but it is strongly recommended.
Without more facts, it is unclear what all of your options are. It sounds on the surface as if there may have been some kind of dispute involving the 15 year old and the Father. Without more details of the situation, it is hard to advise.