There is no absolute standard for the length of a 15 year old boy’s penis, and there are usually different reference standards for penis length for men of different ages, and the length of a 15 year old boy’s penis is about 6 centimeters when it is soft. As men grow and develop, the sex organs are also in the process of development, the length of the penis is related to age, physical condition, personal constitution, heredity and other factors, at the age of 15 years old, the penis length is about 6 centimeters when it is weak, and the penis is longer when it is erect. If in the process of growth and development, the penis is too short, and the development of other sexual characteristics is significantly slower than the same age, you should go to the hospital urology department in time for consultation and treatment.