You did do good work (having done similar myself, but I weigh 135 and the trailer/bike/kids weighs ~110, so I do not have too much power to spare going up a rise. As for the calorie countr I would not put too much faith in the values that you get out of them. Despite the emphasis on weight, one of the key factors is the added wind resistence because efficient rolling weight on the flat take very little work. When my daughter was younger ~25-30lbs I would ride the 25-mile Paoli Loop (rolling, not too hilly but with several noticable pitches with single-digit speed) and maxed out at 19 mph using my road bike. I doubt that I was capable of maintaining 1000 calories/hour for 80 minutes (my guess is 925/hour) so that is one reference point for actual work rate.

I think that calorie counters often "over weight" weight and "under weight" the effects of speed (speed-squared effect of wind resistence) without adjustment of the aero effects of different "rides." The 815 is probably not too bad; my guess is it is high but not by much. One standard is that for a normal athletic male, running (or walking) a mile takes about 100 calories -- thus, were you averaging about 7:20/mile effort for the entire way. Running can usually burn more calories because you are not sitting down. I had a slightly extended discussion with a rider that got a calorie count of ~1475 for a ride of about 20 miles at 15.5 mph