I really don't recommend trying to stop and rest on a 15% or more grade with any intent to start again. The ground angle is steep enough that you can't necessarily rest over the top tube, and you can't necessarily get on and off the bike safely. The bike handling skills required to stop and rest on that kind of grade are pretty badass.
There is no shame in walking the bike. None. If you walk up and down the hill regularly, biking does get easier.
There is plenty of shame in not trying hills, coz if you don't try, you won't get stronger. And there is nothing like a good hill for developing speed.