I too would recommend following through with the speech consult and hearing eval and go from there. Like the others have said, there is most likely nothing to worry about. OTOH, I think that what we feel as parental gut instinct is very important too - you're worried enough that you came online and posted, and you've asked your dr. Your dr. saw enough reason to give you a referral. Again, chances are it's nothing, but if it *is* something you'll be very glad you're on top of it this early in your child's life.
FWIW, my ds wasn't speaking at 15 months. At the time I didn't think anything of it - he was my first child, I knew I didn't start walking/talking until later than most kids, I knew Einstein didn't start talking until he was three. I never asked our ped about it, never thought to ask about it. Our ds did understand and use signs. He was also our only child at the time. I'd have been quick to say "why does he need to talk?" and was quick to think "there's a wide spectrum of normal when it comes to early milestones". When he was around 3 years old, he suddenly started talking in huge, miles-long, complex sentences... so again, we just assumed he was a quirky smart kid who hadn't needed to talk when he was little. Then school hit and his world imploded. We eventually found out he has Developmental Coordination Disorder and an expressive language disorder - both of which we had some very obvious clues about yet never saw in his early developmental history mostly because we weren't looking for it. One of those important clues was late development of talking and, in his case, lack of babbling. He's doing great now, at 12, but please know that there were many times (and still are) that I'd give anything for him to be back at 15 months old and have a speech eval and early intervention!
Best wishes,
polarbear
