As TJ said use the watch. Evinco tires do tend to wear the way you describe due to the shoulder geometry. For a cadet running blues flip the tires after a full day at the track to reverse the inside and outside edges.
I assume you mean 1.5mm on the snipers and not 1.5 degrees. 1.5 degrees would be a massive amount of camber. If you due the math quickly and we assume that the snipers are 30 inches apart when doing an alignment 1.5 degrees would be 20mm. On the other hand 2mm on the snipers at the same distance between the snipers and you get .15 degrees.
Adding the positive camber to drive tire wear as you have tried will increase grip up front and throw off the front to rear balance in the kart (as you have found). Remember these karts are mostly designed in Italy and the euro run a narrower front tire. The rears are still the 4.6″ we run but the fronts are about an inch narrower. So when the kart is run with 4.6″ tires all around the cadets have a massive amount of front grip. Imagine driving a full size kart with 7.10″ tires in front. when my son was running a birel cadet we would typically run 2-4mm negative camber per side.