I think it is for most of us, especially for those who are playing on relatively level courses and go someplace with a lot of elevation change. My home club is pretty hilly, so I've learned to evaluate up and downhill shots better than ever before.
Yes lol 15 feet. Now you see why my golf game struggles. It is very difficult to judge. I try to use trees as my guide but that doesn’t help on links style courses. At best it’s a guessing game for me.
For better or worse, there's no good (legal) way to actually measure the actual elevation change up or down, its all got to be eyeballed, unless you want to use something like Google Earth ground elevations in advance. But 15 yards, 45 feet, is a pretty big elevation difference. Do you maybe mean 15 FEET elevation change for a one-club difference? That would be closer to what I use.
Go up or down a club per 15 feet up or down. Now there are still variables like you are on a par 3 155 yards and 45 feet down. You wouldn’t club down 3 because you still need to hit it close to that distance. That’s the measurement ive been given by a couple different PGA teachers.