If it's dry (and has been for a few days (like that's going to happen!)) then normal shoes are fine, but if it's wet then a bit of grip would certainly be beneficial
15 MILES !!?!!?? I haven't even made it to double figures on the flat for 3 months thanks to injury. I'm now officially scared
Incidentally, don't know if anyone else has noticed but it looks like the stretch of the A24 leading to Ryka's will be closed from 8pm for resurfacing so a fairly long diversion may be in order for people leaving after then. I was fairly confident of getting away in time but .... 15 Miles!?