If it's of any help with your selection, even on a dry day with warm rear 285mm x 18" tyres I still spin up (occasionally) in 3rd gear (with a 3.63 final drive in the gearbox). That's with just 340 ft/lb of torque.
I would imagine your torque is the same as mine, so with just 235mm tyres AND with the added torque of 15" wheels you will be spinning up all the time at a guess. Food for thought.