If they feel better and handle/balance nicely, then 22" is better.

The velocity loss is minimal, like about 50fps or less and not important.

The whole idea for a double rifle is to have a quick handling rifle with 2 shots available without having to reload. To be effective for this, the gun must fit and swing like a slightly heavy shotgun - say similar to a 10 bore double. I really liked mine on geese - heavy enough at 9 pounds that I couldn't stop the swing if I'd wanted to. It was deadly. That's how the rifle should swing- instinctively.