Dear B.
I am a huge proponent of utilizing your pediatrician to the max capacity. if you have a question, call and talk to the nurse........that is why they are there. if you are concerned..........ASK THE QUESTIONS and let the experts determine if there is a need for concern.
i have two separate friends whose sons did not walk until between 15 & 24 months. one child is completely "normal" and was just slow to walk b/c he was a heavier weight little guy. the other was normal weight and has significant developmental delays in speech, hearing & mobility.
not in any way to alarm you that your child is facing these challenges, but just to encourage you to consult your pediatrician.
good luck!