I agree with this. Being that the MP57's are less forgiving, they would force you to "swing better" with the instant feedback that you get from a bad swing. I find game improvement irons give a false sense of securtiy with a swing. If you hit it bad, it still flies good...that in my opinion is not a good measuring stick to where you are in your swing.
Also, the difference in feel you are experiencing could be two things. A forged feel with minimal offset vs. a cast feel with a high offset (way less of the butter feel with a cast club) and the center of gravity on the club. The center of gravity on the G15's are much lower (promoting a higher ball flight) than the MP57's. That means that you will have to hit the club lower on the face consistently to get that nice feel.