Can’t help but compare

My son is about to turn 15 months. My best friends son is 4 weeks older and can recognize animals and makes sounds, recognizes colors and body parts and says a bunch of words and just understands alot more. My son doesn’t do any of this and it’s starting to worry me. He says mama dada and babbles but that’s it. I practice with him all the time but I can’t help but compare. I know every baby develops differently and at a different pace but I’m just amazed at how much he doesn’t know compared to my friends son. Can someone give me peace of mind ?