Out of combat, "per encounter" means "Every 5 minutes".
So, for cliff climbing...not so much.
Even if it were 'at will', you can still do it only once every 6 seconds, and that means you'll fall the full 15 feet LONG before you get to do it again.
At Will: Once every 6 seconds.
PE: Once every five minutes.
Daily: Once every 6-hour rest period but no more than once per 24 hours.
Other than the VERY rare case of an encounter lasting longer than 50 rounds(!), this provides a good basis for working out the effects and impacts of abilities. A wizard can use his at-will powers 600 times an hour, for example. Depending on what kind of powers there are, this can be pretty world-changing.