Not done that but when I was in Ecuador I visited Chimborazo (fun fact, it is the part of the earth's surface farthest from its centre, even further from the centre than the top of Everest!) we got a bus to the camp at 4800m/15,748ft and walked up toward the next camp at 5050m/16568ft. Only a small rise in elevation yeah???
This is probably the hardest thing I've ever done, the air never ever is thick enough to breathe. Even sitting down it takes ages to catch it. You walk a short distance, then stop and breathe. Repeat. I'm no fitness pervert but altitude doesn't care. Some people can make red, oxygen carrying blood cells, more quickly than others. It's a body thing, not a "I did 500 reps in the gym thing".. I saw really healthy, quinoa and lentil types having to get on oxygen whilst we sat and had a beer and a fag.
The moral or this ramble, don't do this sort of thing lightly and do get some experience at altitude if you can, because it's not to be trifled with and severe altitude sickness can cause real problems quickly, and dump all over your plans.
All that said, do it!