So her parents take her to the doctor to be examined??

Mornings plural, how many?
This is impossible to advise, even knowing how many.
I'm 64 and have heartburn all day long.
Pregnancy, you wonder? Far too many variables. You take a test.

OK is the 15 year old having sex, do you think pregnant ?

Could be ulcer, nerves, pressure and stress.. Really not enough info given

Could be the flu, could be pregnancy (if the 15 year old is sexually active), could be something else.

Even with more info we can't give you a diagnosis over the internet. Not even a doctor can do that.

See your doctor.

Good luck.

Notice that the original question has been amended quite a bit since the above 4 replies.
PLEASE go to a doctor, or explain why you won't, using Answer.
Conditions that come to mind such as ulcers are best treated sooner rather than later! There are PLENTY of things it could be, some common, some rare. You didn't even mention vomiting or a month of this when you first asked. Given her age, appendicitis (most common in ages 10 - 30) would fit her symptoms, which can appear as pain just about anywhere in the abdomen. Once it bursts, it's a severe emergency.