Having tried the 1.5" on a quartering away shot that got liver and probably only one lung, I wouldn't use any two blade less that 2" again. Penetration wasn't an issue. It blew through like it hit hot butter from 54 yards, and even blew through the offside humerus and went another 20 yards into the ground. But we lost the blood trail after dark, came back in the morning, and found where he last bedded but was gone from there. Not another drop of blood after that. Eventually found him much later 300 yards from there in a brush filled ravine that was about 120 degrees off of the direction he had been going.
I've had several similar shots with 3-blade fixed and 3-blade mechanical heads and those elk haven't made it 100 yards. Not sure how the 2" would have done in the same situation, but it certainly couldn't have hurt. Completely broadside........I'm sure the 1.5" will work just fine though.