Memnon, the M15 had the M3 chassis.  The M19 was a tracked M24 chassis and didn't see any field action in WWII.
What I don't like about the M19 is the number of rounds, and the openness of the gun mount.  If you thought the Osti turret was knocked out easy. . . 
It is an impressive attack vehicle though.  The AP rounds could penetrate 40mm of armor at 1000 yards and the HE rounds could go to more than 22,000 feet or a range of 4.3 miles.  WOW.  But with only 12mm of armor in front, it would be a quick kill in AH2.
LTARsqrl