My son is 15 months old he is not walking?

OK. Many children walk late. If you have been seeing your pediatrician for regular health care visits and he/she s not concerned, it could be your child is just a late walker. If I have a patient not walking by 17 months I will get a physical therapy evaluation. Many children will have advanced social/language (talking) development first and their gross motor (walking) will come a little later.
What can he do? If your child can pull up, walk holding on, and stand without support, he is most likely normal. Some children are a little fearful of taking off on their own. Give it another month or two. If not doing these things, a physical therapy evaluation will help determine the reason.