A big congrats to you... 15 weeks down!!!
Your belly will pop out soon enough and you will be feeling the little flutters, pushes and kicks before you know it!
My auntie didn't feel pregnant until she had a decent sized belly (as it was her first bub she didn't feel it until she was about 24 weeks preg)... Everyone is very different and every bub is different... It'll all happen it good time
Take is easy and enjoy the remainder of your preganacy