Lol he's only 14/15? Boys tend too shoot up at around 15/16 in a growth spurt because they grow physically taller at a slower rate then girls who tend to have their upsurge at around 12/13 - of course that's just general though and there are plenty of exceptions.
But then again, maybe he just isn'gt going to be very tall btw time he finished growing in height - the average height for men is 5ft8in I think so he's not too far away and still has time to make it 😉