well, 15kg is pretty hefty My DS doesn't even weigh that. Still, at around 14kg he is practically weightless in my beetlebums. There are sooooo many options out there. The hard part is just finding the one that's perfect for you. Those with back problems probably would need to be a little pickier about what they choose, but I think many can still find something comfortable.

Kaytee, I'm certain you can find something that would suit
The hard part can sometimes be limiting yourself to only one carrier! Because so many different types and good for so many different situations and different children. (at least that's how I justify it to my DH).