Based on the more than 5 year disparity in age, he could be charged with statutory rape. Paternity can't be established until after the baby is born. Then, a Petition to Establish Paternity can be filed by you in order to require him to take a DNA test to determine if he is the natural father of the child. At the age of 15, you really need to have the assistance of family and friends in raising this baby. Basically, you are still a child under the law raising another child.
The information provided in this answer does not create an attorney-client relationship and is not considered to be legal advice.