C.A.
I've noticed (from my family and friends) that this is a very common concern. The 15 minutes really does make a huge difference. I use to put my daughter on the changing table or crib with her head at different ends so when she looked over it would rotate the direction her head would turn. Or when I'm playing with her and she was lying on the floor, I would go to different sides. The head is very soft right now and forms easily. If your doctor isn't concerned, I probably wouldn't be. If you are, take him to another doctor and get a second opinion.
Best of luck and enjoy this time!