Whether or not a 15 1/2 year old boy can still grow depends on whether or not his epiphyses are closed. For most 15 and a half year old boys, if their epiphyses have not yet closed, they will still be able to grow taller; if the epiphyses have closed, they will not be able to grow taller.
Height is closely related to genetics, environment, nutrition, exercise, sleep, individual differences, etc. Generally speaking, if the epiphyses have not closed around the age of 15, there is still plenty of room for height development.
If the epiphysis has closed, you can’t grow any taller after 15 years old.
Adjusting daily habits, supplementing high quality protein and calcium; proper physical exercise and enough sleep are conducive to growth and development.
If you find that your child’s growth is slow or has stopped prematurely, it is recommended that you go to the hospital for an epiphyseal examination to determine whether there is still room for growth.