Hey Megator, you still have a pretty cool track car! Enjoy Spa, and I really hope you get a break in the weather. Been wet and cool lately.
I have the standard 4 piston 15" brakes, and I think that with some decent pads (PFC 08s on the way) and Castrol RBF fluid It will be enough for the car. I tracked a 2014 Mustang GT which was heavier and faster with stock 14" 4 piston Brembos with good track pads and fluid and braking was solid.
M2 is lighter and less powerful so I would hope the standard M2 brakes suffice.
Good luck next week, have fun at Spa and let us know how it goes!
Good way to pass the time while you await your M2C.