Perhaps you should indulge your son on his birthday/xmas with a mid range digital camera to get him started off. Looks like you know a fair bit about photography so could help him out....
I assume he (like most 15yr olds) is interested in driving/cars. A trip (father and son) to brooklands, MB world in Germany, Gaydon Heritage centre to see cars, and maybe indulge in the driving of them, with some photographic memories would be a nice thing to do and see him started off.
I particularly liked the one in B&W-captured the angle of the car perfectly