It is completely normal to have a flat stomach and not feel any baby movements at almost 15 weeks of pregnancy, especially if this is your first pregnancy. Every woman's body is different, and it can take longer for some women to show or feel their baby's movements. The size of your belly will depend on various factors such as your body type, the position of the uterus, and the amount of amniotic fluid present. As for feeling the baby move, most women start feeling those fluttering sensations between 18-25 weeks of pregnancy. However, it can vary from person to person. If you are concerned about the lack of movement or have any other worries, it is always best to consult with your healthcare provider who can provide personalized advice based on your specific situation.