If you are going to buy Health insurance provided by the university, then I advise to buy Travel Insurance till you get registered for college. You are officially considered as a student of the school after attending the orientation.
If you arrive in USA 15 days before orientation, then you will NOT have health insurance from college for those 15 days. So, make sure you get travel insurance coverage for those 15 days.
Refer to the link below to buy the ISO insurance if your university gives an option to buy your own health insurance.
Link to Buy Health Insurance :