I mixed up some 115 and 147gr. in a mag to see if there was a difference. The lighter bullet has a snappy recoil where the heavier bullet is softer with less muzzle flip.
I've been doing the same thing, and noticed the same thing. I also mixed up some 124gr in there. I've settled on 147gr myself. When I tried 124 & 115gr my shots were quite bad, I'd say due to having gotten used to the 147gr. They make bigger holes in the paper too because American Eagle's 147gr bullets are a truncated cone shape.