Al,
C-15 mileage is at best 6-6.5MPG. Also twin turbo vs the C-12 single turbo. I would be more concerned with the Kongsberg Chassis Control Module system. Currently there is no support for the module. Do some research on the system, on some of the other forums, then you can make an informed decision. It’s a beautiful coach, good luck. The Monacoers forum has lots of info for the Kongsberg CCM.