My small hunter is a big 15.2 but looks small in a small hunter class. Can't really comment on this horse, he does take the leg, the rider may be small but he does look big.
I don't think you can say that a horse is worth less as a 15.2 when it would be eligible for a range of Intermediate classes as well as small hunter. At 15.3 a small hunter type is a pointless beast really, only really suitable as a worker, but too small to be competitive unless outstanding, too chunky to be a riding horse and too small to be a show hunter or midleweight. So there definitely is a financial reason for ensuring the horse stays under 15.2 - it will be worth far more as a show horse.