My best advice to you is trust your gut instincts. My son was not talking at all at 16 months and I knew something was wrong, but I didn't trust my instincts. People kept saying, "he's a boy, don't worry so much, all babies do their thing on their own time." But I could tell there was more going on. My pediatrician did not want to refer me to a speech therapist to have him evaluated. By 18 months, my son was still not talking at all and finally my pediatrician gave in and gave me a referral. It turned out that my child had a very severe speech delay and also had what is called sensory integration disorder. He's 4 now and doing much better.
At 15 months of age, a child should have 10-15 words, by 18 months of age, a child should have about 25 words (according to the speech therapist we worked with for 2 years). By 2, they should have about 100.
Chances are your child is just a wee bit behind and he will catch up in no time. BUT, if you feel something is wrong, it does not hurt to push for an eval or call ECI for a free eval. You know your child best and don't let anyone make you think otherwise. In the meantime, I highly recommend picking up the first Signing Time video or DVD - it is the best way, IMO to teach kids the basic signs and to learn them yourself in a very fun and engaging way. It helped with my child immensely.
Feel free to contact me if you have any questions, I have been through a lot with my son and am pretty knowledgeable about speech delays and speech therapy! :) Good luck.