Time for a second opinion - consult another physician (separate from your present doctor's practice, if she is in a group practice). If the child is healthy and hitting every milestone and is small all over, why on earth would a doctor think an MRI is necessary? Based on what you've posted, there doesn't seem to be any medical need for it, other than a chart that your daughter doesn't fit onto - no symptoms, no call for alarm. An MRI would likely be a traumatic experience for a 15 m.o., plus it is a very expensive test. Ask your doctor to explain precisely why, in plain English, she thinks such a test is necessary. She should be able to give a straightforward, clear reason. Call your insurance company and see whether they would even be willing to pay for such a thing. Also find out what your doctor has actually written in your daughter's medical report and what she has been submitting to your insurance company. If either of those records do not correspond with what you're being told verbally by this doctor, it's time to switch doctors.