Barring breaking the game itself, there is nothing a level 15 character can do in an encounter that challenges a level 22 character, and there is no challenge in an encounter for a level 22 character in an encounter that a level 15 character can contribute to.

There is in essence no game here.

If you would like to sit around a table and tell stories to each other with no mechanics to back it up, feel free to join in that non-game of D&D.