By a 15m a kid should use 3-5 words, point to one body part & retrieve an object on request.
The quality of their words is meager. Strangers often understand about 50% of their utterances at 2, 75% by 3 and 95% by 4. If the kid appears delayed you can contact the local early childhood contractor for a speech & language evaluation. The kid also needs his doc to assess his/her hearing.