It is completely normal to not feel your baby move at 15 weeks in your fourth pregnancy. Every pregnancy is different, and the timing of when you feel your baby's movements can vary. In previous pregnancies, you may have felt the movements earlier due to factors like a thinner abdominal wall or increased sensitivity to the sensations. Additionally, if you have an anterior placenta (placenta positioned towards the front), it can act as a cushion and make it more difficult to feel the movements early on. As long as you are not experiencing any other concerning symptoms such as severe pain or bleeding, there is no need to worry. Most women start feeling their baby move between 18-25 weeks of pregnancy. If you still haven't felt any movement after that time frame or if you have any concerns, it's always best to consult with your healthcare provider for reassurance and guidance.