What kind of food, fruits, drink to give 15 month. Till now he doesnt have any teeth. How

Even if he doesnt have any teeth, but his chomping skill is good, you can consider giving chunky porridge. Soft fruits like kiwi,papaya, banana are good soft food for them to try too.

No worries about the teeth. May possibly be a later bloomer and that's fine. Give him normal food, he would be able to eat.

Do not underestimate their gumming power