So, you burnt thru a whole hopper, 47lbs, in a little over 10 hrs? Your wife got home at 6, you filled it before leaving at 8am. Probably a 5 lb/hr burn rate? Or about 40k btus. The stove still has some capacity to burn more, since it's a 52k btu stove. Having said that, 67 degrees is not bad, I don't heat my house beyond 65.
A 148k btu furnace seems largish for your house, maybe indicative of your heating needs. 1500 gal of propane is about equal to 1000 gals of heating oil, which is above average for a 2000sqft home in Maine. Nowadays, the avg is about 800 gals, so your heating needs seem to be a bit above avg, though if you are including DHW in that 1500 gals of propane, that could be the difference.
I'm going to guesstimate that you probably used about 9 gals of propane on an "average" winter day, which would put you at about 2.5 bags of pellets for an avg winter day, which is a lot. I'd guess the average winter needs for most people here is around 1.5 bags. Remember, that's for an average day between 25 and 35 degrees.
So, now that I think your house has higher heating needs than your avg home, there are still a couple questions. One, if you are supplementing your heat with the gas furnace, are you actually turning off the stove because the stove thermostat is reaching its set point? I know you tried manual, but I want to make sure you're not inadvertently turning off your stove because of the gas furnace being on. Two, are you sure there aren't air leaks around those large windows and doors? You should consider getting a cheap IR thermometer and shooting the picture framing around the windows and doors. If you find any, remove the moulding and foam. How's the snow melt on the roof? Do the rafters show thru as the snow melts? Does your roof keep its snow hat on longer or shorter than your neighbors? I know you have what looks like a 12:12 pitch, so it might slide off first.
One of the downsides to an insert is that the hopper is not all that large. So, if you burned at your max rate of 6.5lbs / hr, you'd have to refill it every 7 hrs.