well said Mamofwill! I agree. just focus on Imput, don't worry about seeing results. It is unlikely (but never imposible
) that a 15 month old will sing a chord with perfect pitch and then move over the his fisher price piano and play a concerto.
I do agree though that the more enthusiasm you show the more you baby will copy. Over all I suggest you just keep going until your child is older and regularly communicating in a variety of formats.
Enjoy the time.