Most people first start their period around age 12-13 years in the United States. Some people start earlier, and others start later. Everyone is different. The timing of your period also depends on how long ago your breasts and pubic hair started growing (when you started puberty). Usually, people get their period 2-3 years after starting puberty.
There are many reasons why you may not have started your period yet. Maybe you started puberty at a later age and will start your period soon. It could also be that your body is making too little or too much of certain hormones (chemicals in your body). Some people do not have enough body fat to get their period because of not eating enough or exercising too much.
Since you are 15 years old, it would be a good idea to check in with your health care provider to talk about why your period hasn’t come yet.