first, if you're low and slow, don't be doing too many steep turns. will be uncomfortable for your sightseeing pax (is a very quick way to make them feel queasy), and there's not enough fat in the airspeed/stall equation, especially as you're obviously not overly experienced in the aircraft. very easy to get into a stall in the turn situation. personally i'd be setting 2200rpm, whatever MAP it takes to maintain 85-90kts, maybe even 10 deg flap if you're that way inclined (will give better forward vision at least) and keep the bank angle down to 30deg max.
my 2c........