Is there a significant advantage of the 2015 over the 2012, given one can get one with better mileage at a better price, apparently of essentially the same car? Doesn't the fact that priuses are considered so reliable mean that it wouldn't command a significantly higher resale value?
It depends on how long the OP plans on keeping the car. To me, a 3 year advantage for the '15 in terms of hybrid warranty is worth a lot. I think the OP's state is a CARB state. If that comes with the 10/150k miles warranty, a Prius could be covered until '25. Plus, the '15 would be after the mid cycle refresh.
Mass is a CARB state so the 10/150K warranty applies. The 2012 was the 1st year of the mid cycle refresh. The most notable feature that the 2015 has over the 2012, the back up camera was standard in all trim models.
A lot of short trips? Hilly area? Average (calculated) as reported by owners on Fuelly is around 45 mpg.
The graph above shows that 39.9 mpg seems to be as common as 49-50 mpg for fuelly owners. So apparently, that's not out of the ordinary in real world driving. I agree that the length of the commute is key. If I have to hop on the highway first thing in the morning, I don't hit 39.9 average for my drive until after 5-6 miles- so short trips from a cold start definitely will kill mpg. However, the overall fuel costs will be lower due to the short drives. The weight of added passengers reduces mpg, also. I added a couple of passengers on a typical 50 mile trip yesterday, and my mpg went down around 10% for that day. It's also worth mentioning that the impact of short commutes, cold weather driving, and added weight will be similar to other vehicles, too. Probably more so in stop and go traffic.
I bought a 2015 Persona back in June thinking it would get better than my 2005 which I averaged 45-46 mpg. I've been pretty disappointed as I average 40-43 in the summer and I'm down to 37-40 in the winter here in the Pacific Northwest. I even went so far as to trade someone my 17 inch Persona wheels for 15s. Pretty bummed about the mileage... I expected to get high 40s if not 50. Of course I do have a lead foot so....
What are your 15" tires, and what were the 17", if you recall? If both the 17" and 15" were decent for rolling resistance, I'd be interested to know your impressions, what going from 17 to 15 did. We actually do that every fall, going from 17" Michelin Pilot MXM4 (which at least with ours have the Green-X logo) to 15" Michelin X-Ice2, but that's sort of apples/oranges, with the latter being a snow tire.