Are you SERIOUSLY considering killing the efficiency and voiding the warranty on the boiler to save the cost of the ss liner?
At $4/gallon oil you'd pay for the liner in one heating season on the difference in efficiency!
To get better burn times either raise the min to 170F and design to 200F- whatever it takes, or increase the hysteresis (differential setting) around the setpoint (I haven't looked at that controller) boost it to the max. You apparently don't have enough radiation to emit anything close to the full boiler output at 150F, and the short-cycling at 2.5 minute burns pretty much kills the efficiency benefit of the outdoor reset. Ideally you'd get at least 10 minute burns out of it, but even 5 minutes might be enough to bring the chimney up to temp.
But get a stainless steel liner and crank the temps back down when you can.