Looks a fine machine - impress the clients.
Trouble when you get too fast is that you can burn certain carpet pile. Keep the machine moving.
Up to 230rpm is ok for carpet bonnet work, but you need to keep the pads and carpet moist. Some cleaning fluids have more lubricant them others. M-Power and Nemesis are good.
15" is not a problem, mine is 15" and I buy 17" pads for it, no problem. Yes, on big commercials you may be better with bigger, but then 20" is better then 17".