It's normal not to feel fetal movement at only 15 weeks. That's not even five months yet. Most women don't feel fetal movement until AT LEAST 20 weeks. None of my sisters-in-law felt movement until their 6th month. Most of my friends didn't feel movement until after their 20 week ultra-sounds.
It's possible you already are feeling something. It would be fluttery, like butterfly wings or blowing bubbles in milk. It wouldn't even be nudges or bumps yet. It's just too early for that. I felt that at 13 weeks with my eldest daughter, and she hasn't stopped moving yet. That's pretty unusual.
With my second pregnancy I felt her around 18 weeks. She wasn't very active, but she also hung out around my spine a lot. She tended to move away from loud noises, pressure, and movement around my belly. I'm sure her positioning played a large part as well as just not being an active baby. She was the same way when she was born.
With my third pregnancy my placenta wasn't positioned properly. It was too high and that affected feeling movement aka I couldn't feel her moving. I couldn't only detect movement if my hands were on my belly and she kicked my hands or I put an object on my belly and she made it move. I had to go to the OB office frequently to hear her heartbeat and for non-stress tests with ultra-sounds to make sure she was all right on a bi-weekly basis for a while, and then once we diagnosed the placenta problem we dropped it to weekly with just NST's. This went on for three months.
We did it that way with my last pregnancy because I was worried that I wasn't feeling movement at almost six months. It was just a realization I had when I had a moment to sit still while one child was at preschool and the other was in first grade. I called the OB and told him my worry, and he was happy to accommodate me to alleviate the worry.
My point is that if you're having debilitating worry that you can't let go then call your OB. They should be happy to do a check up for you or reassure you that you'll be fine until the next scheduled appointment. If they choose to reassure you, then make sure you can articulate what it is you're worried about. If they can't reassure you then make sure they know it. A good office will take that seriously.