There's a guy in our church who used to do a lot of elk hunting until the calendar caught up with him. He bought a gorgeous black mule for packing - all 17 hands of it. When I saw it I told my wife that he wouldn't have it long. It would take a forklift to load an elk on a mule higher than his head. That's exactly what happened. He packed 1 elk and decided that 15 hands was a lot more workable.
I had the same trouble with a 15 hd one. I traded her for a 13 hd one. Sure was a lot better. I had a couple 16 hd Tennessee Walker mules too. Same thing. Now I ride 13&1/2 hd one.
Many people, new to mules, make the mistake that they need a mule as big as the horse they were use to when a smaller mule can do the same work.