if your airplain is rolling to the right witch is diferent than a snap it has to do with the propeller
you do not notice it on a 40 size because you have a small prop
the gyroscopic forces of a 15 inch prop are huge
enough to roll your airplain over
my 15 pound midwest cap 232 dose the same thing if i pull to hard it rolls to the right
my friends full size super d exibits this behavior also
when i pull hard on my cap i get about 1 quarter of a roll out of it
you can test my thery witch i got out of an aerobatic mag
just pull out of a dive with the engine off or at idle
try a wood prop if you want to reduce it
you cant get rid of it unless you go to contra rotating propellers or a jet engine