They have daily flights if you can't make it down JUST KIDDING!
I don't believe that distance equals distance, meaning I wouldn't worry that you're only doing 10 mile practice hikes, and "the event" is 22. What I would say is more important is the type of practice, and your body's tolerance to altitude.
I would say practice on hilly areas, and do A LOT OF STEPS, both up and down. Also, having a pole or poles can help. I only needed mine on the way down.
I'm moderately fit and had tired legs at the end, but they hurt for many days after.
