J.C.
He should not be night feeding at 15 months, mine stopped this at 2 months. Babies wake at night to eat at older ages, not because they are truly hungry or need to eat, but because that is what we have trained them to do. Now you have to re-train him to do what he should be doing at night, which is sleep. If he wakes, give him a chance to self sooth (like 5 minutes). If he does not, than go in and comfort him, but not with food. Having a bottle in bed at this age is going to rot his teeth. Just sit with him until he is calm. It may take a few nights for him to understand and adjust to the change, but it will be well worth it.