Just wondering if the jaw can get infection from simple molar extraction 15 days after tooth removed?

Yes: It's possible. If the extraction site were not completely closed over, an infection might have been brewing and then make itself apparent at that time. It is also possible that you don't have an infection or do but from an adjacent tooth. See your dentist to have it evaluated.

Possible,: Usually, infection present but not clinically bothersome until symptoms develop.

Yes: If food or debris got into healing socket than possible or if a root or piece of bone is present than yes.If a diabetic or compromised immune system than yes.

Yes, of course: You should see your dentist ASAP if you have signs of infection after 15 days post tooth extraction.

Infection: Infection can stem from multiple sources. Most probable is the infection in the tooth that caused the tooth to have to be removed may have spread to the surrounding bone. Gums may have been infected. Clot may have washed out resulting in bone infection (dry socket). If upper molar, may have pre existing sinus infection. See yourtreating Dentist or Oral Surgeon for support.