Well, as in my original post, with my O-320 I'm only getting 75% (120hp) power at 6,000ft, and at 1200-1500fpm climb, I'm there in 4-5 min.
I rarely fly lower, unless it's just to fart around the area or grab a nearby $100 burger.
The 141hp of the 915 at takeoff is 88% of an O-320, so I assume...