15 weeks is a little early to feel movement, dont worry! I started feeling movement at 19 weeks. Im 25 weeks and there are some days my son wont move since he doesn't have much room to kick and stretch.
People don't start feeling their baby move til at least 16 weeks everyone's different some people don't feel move and kicks til 23 weeks... everyone's different. Don't worry your fine
I'm 23 weeks and I didn't feel movement until 21/22weeks, you placenta may be at the front which will delay feeling movement was one, your midwife may tell you what postion your placenta is at your 20 week scan, my stomach has only recently started going harder