You really need to define your gearing, however, I live in the wasatch so 15% on my first bike (standard double with 12-25 in the back, so stingy for sure) was fine with practice. All you do is find hills and ride them, try less steep hills for practise and work up (try map my ride for route planning, and I would only use a garmin with barometric as a reliable indicator, not strava or MMR on the bike) and keep trying at your steep bit, I always stay seated unless I feel I am about to fall.
so things you should answer first:
what kind of bike (including weight etc)?
what is your gearing? What gears are you using? (this might be a dumb question, I never have enough gears LOL, so I never have any left, but people so strange things)
The thing that helps you in hill climbing is hill climbing, weight loss if you are heavy, and optimal gearing would be nice. My most recent bike is standard double with 11-28 so it is nice to have a bit more range for sure. I have never ridden a triple or a compact, but my friend has 11-32 on her cassette and it is lovely to watch her spin up the canyons, but I am always faster LOL. I am a masher by nature though. When I climb, say canyons, I try not to look ahead to far, take it a bite at a time. I don;t really have short climbs so I do think the longer climbs really help. There is nothing wrong with stopping and unclipping and taking a breather but not on 15% because it sucks to try to get going again at that point.