Is my cat overweight or just naturally burly?

I adopted a girl few months ago she is still less than a year old. She has turned into a burly cat. Like a janguar. She’s stocky and powerful. And heavy got to be 15-20 pounds I think. She has a belly pouch that flaps when she runs already. She seems built for wrestling. Or maybe she is just way overweight. She isn’t graceful going up the cat tree it seems idk. Can’t tell if she naturally a Pumba rather than a Nala.