The Cameo can only squeeze in 13 inches max,
Most vinyls have a grid on the reverse so you can slice off a straight line, if your cutting down to seven inches off a 15 it may be a problem (I'm not sure because I am not in the shop) The rollers may not slide over far enough,, they do go over to 8 inches because that's an A4,, perhaps someone with a machine in front of them could measure and confirm?
MDP in the UK supply on 330mm rolls which fit the cameo holder nicely