I have friends who just hit puberty at 16! Don't worry, yours will definitely come :) And actually, be glad it's taking a longer time... Some things are less troublesome without puberty in your life, you'll know what I mean when you have it XD
But I understand that when you don't have it and your friends do, you'll feel like you want it to come. Just be patient, it will, and actually enjoy the remaining time you have before it hits ^_^