Why does it take 15 minutes to listen to my lungs when I go for a check up?

Hard to tell. Depending on the practice setting (ppo/private practice, hmo/private practice, large/busy group practice, public clinic) a doctor may have anywhere between 10-30 minutes to see a typical patient. If a patient feels his doctor is spending too much time on one part of the exam, the patient can try another doctor to compare the service he receives from the two doctors.