You are 100% fine to be riding a 14 - 15 hh Section D, if you're worried about the weight issue, then don't be, you will be fine.
If you're worried by the look of it.......well that is something that you have to settle in your own mind. As others have said, a good well sprung Section D will take up a lot of your leg in its barrel, so your feet will come at a sensible level.
One thing I have learned with advancing age..........to h3ll with what anyone else thinks about how I look, if the horse or pony is fine with my weight then I'll ride.
Here is a pic with all my current riding horses
Bert is nearly 17hh,
Appy G 15.2hh
Ace, 15hh on tip toe
Fancy good solid 14.2hh
My height remains constant at 5' 9" and my weight varies between, around 230 pounds in the pic of Fancy, to a wonderful 175 pounds when I'm on Ace.
I feel fine on all of them.