I think i'm too tall for my horse?

I deffinatly do not think you are too large,
I am 5"6 and riding the same hight horse.

I am 5'7. My mare is 15.1. I fit her perfectly, you'll be fine. =]

My horse is short, but I'm short as well. Hehehe...so I can't really help. But I'm sure it's fine. I see girls at my barn riding freaking ponies and they are tall, racing around the ring, jumping big jumps.

The horse I ride is 15 hands and I am about 5'7'' or so and I don't feel too tall for him.

Height is not a big issue unless your insanley tall riding a tiny pony1 it the weight of you and the weight of the horse that matters

I don't think so. Im 5'8" and I jump on a 15 hand gelding and he does fine.