How long the hose on your secondary reg is will depend on what you are going to use it for.
If you are going to donate it to another diver, 22" is awfully short and is very uncomfortable to share.
If you are going to donate your primary regulator, and use the backup for yourself, 22" is fine. But then the primary regulator needs to be on a hose long enough that it can comfortably reach to another diver, and 36" is pretty much the minimum for that. Of course, using a 36" hose on your primary makes a HUGE loop of hose out behind and beside you, to catch on stuff. A 40" hose, routed under the arm and with an angled adapter to the reg, is much better streamlined. And a 5' hose, routed under the arm and then up across your chest and around the back of your neck, is better still.