A.,
If this is a school based public program, speech is without question not all he needs. Request a full evaluation from your school district because you suspect he has a disability. It is reprehensable that a public speech therapist would not have already reccomended that he have a full eval. He should probably be in a program full time that will provide early intervention and therapy.
That is not the whole answer though. You should not depend on public services for all his treatment. Make an appointment with a Developmental Pediatrician on Monday morning. Call your nearest Children's Hospital, and ask for one. This is not a regular pediatrician, this professional will call in every kind of professional he needs, from speech pathologist, ENT, PT, OT, neruology, genetics...everything. They will put all the evaluations into one report and give you a theraputic plan to follow, and you will know what is going on, what you can do about it, and how to help him.
That appointment will be many months away. After you hang up the phone on Monday, call a private speech therapist and make an appointment for an evaluation and start therapy as soon as you can. Do all the homework, and if they don't offer any , ask for it, then do everything you can to help.
Another option is to contact Easter Seals. They may be able to help too with evaluations and therapy. Do not delay, even if you make over lapping appointments with multiple agencies and therapists until you figure out what is going to work best for him. What ever you do, get the comprehensive evaluation.
15 words at age 4 is worrisome, but try to stay calm. Everything you do with your school district should be in writing. If you feel overwhelmed, check out www.wrightslaw.com and check out the yellow pages for Georgia on the Wrightslaw web site, you can find educational advocates near you who can help you get appropriate services.
Get as much therapy as you can, as soon as you can from every source. None of this will be cheep, but it is essential for his development. One of the only things you have that will be free, is time, don't waste it.
M.