I've just been a little worried about being too large for my horse. He stands at fifteen hands, and is fairly thin. I'm almost 5'6" (a quarter inch under) and am about 120-125 lbs. I do english pleasure and some jumping with him.
Am I too tall/heavy for him? I think we look fine, but I don't want to make him uncomfortable.
15hh? No way, unless he has some serious conformation issues. The problem people have too often is that their leg is too long to wrap around the horse's barrel securely. At 15hh, this is pretty unlikely with your height, but pictures would help if you'd like a better answer
I picture would help - especially of the horse. I'm 5'8 and ride a stocky 13.3 hand haflinger. On the other hand I've ridden horses that were taller that I felt too big on - my legs were too long for their barrel and balancing was harder which made it harder for the horse to carry me. So it really depends on their build.
However - I really doubt you are too heavy by any means. It will be more of a comfort and balance thing than anything else.
Defiantly not too big for him, lol horses are really strong and it has to do with ridding them correctly rather than the riders weight. I am almost 5'9", 170lb my horse is 15.2hh and he's the perfect size for me, I also have a plus sized friend who is my height and she has a pony 14.2hh with a back of steel.
I'll ride anything from 13hh to over 17hh, and I'm 5'11". I have and do ride with a really, really long leg, so the horse that would "fit" me by English standards is 16.2hh or better. My favorite horse is like... 15.1hh, maybe 15.2hh? I don't care. I ride child ponies, as funny as it looks. As for how wide your horse is, he'll gain muscle tone with frequent and consistent work and exercise, like any creature. :)
If you're too big for your 15hh guy at 5'6" and 120lbs, then I'm definitely WAY too big for my 16hh guy (who is still growing) at 5'7" and 180lbs. That being said, I'm not too big for my boy at all and he carries me very easily, sooooo I'd say you're nowhere NEAR too big for your boy.