From what I understand reading the posts for the 5th Gen, the early ones had some wind-noise issues with the molding around the front 'vent' or triangle glass, which there is a fix for. (Presumably they all should have been fixed). I would also double check the roof rack, as I've seen one or two, where the gasket is warped, both were 15s.
Of course the interior is more upscale on the 15s, with more soft-touch, and a much more modern head-unit in any trim than the 4th Gen. The 5th Gen are a bit larger, and sit a bit higher....they raised the roof & seat position. One exception is the under cargo area storage, which shrunk in '15, it's now very shallow and doesn't hold as much as the 4th Gen. (Subaru, put the tire changing gear back into spare tire insert, and give us back the deeper storage space!)
On the road, they're pretty similar, although the 15 feels a bit more planted stock, with no modifications, with maybe a firmer ride than a 13/14. (10-12 had the softest suspension, they increased the spring/shock rates in 13, and then re-tuned in 15 again for the 5th gen. The 15s might be a bit quieter, I had limited seat time, and they were close. - But I'm comparing to a 3.6R, which does't make as much engine noise driving as the 2.5, so to my ears they were comparable. The 15 has a bit less road noise, but that could also be the tires. (I changed my tires in Dec of last year, and it made a profound difference). I've done the bigger swaybar and strut brace, which makes the 4th feel every bit as confident as the 5th Gen.
The engine/trans are the big changes. The FB25 went through some changes for the 15 MY, and it gained a couple of horses/tq over 13/14. Some 13/14 suffer from oil consumption issues, which don't appear to plague the 15+ models. The CVT was also reworked and mimics a traditional trans in all but WOT conditions, making far less engine noise accelerating, and a quieter interior during such maneuvers. For '15 even the 3.6R gets a CVT, the High-Torque version from the Forester XT. - Keep in mind there's the CVT extended warranty or campaign on the CVT through 15, if I was looking at a 5th Gen, I'd consider a '16, knowing it shouldn't be affected....and most likely has any other quirks introduced in '15 corrected.
I actually like my '12, as well as the design of the dash in the 4th Gen....maybe I'm an oddball, but I LIKE the faux brushed aluminum on the center console of the dash, with the vents flanking the head unit. My perfect Outback would be to transplant the electronics from a '17 into my '12....I also like the 3.6R/5-Speed combo, it's been used in much larger vehicles, so it should propel a 3600lbs Outback around as long as I keep her. (Same trans was in the Tribecca & used by Nissan/Infiniti in the Armada/QX80, shame it's dead as of '15 in the Outback).
I feel for your discussion, as I went through something very similar. For me it came down to, hey, it's better equipped and a bit less money, and really fast! - My wife wanted me to buy the '12 because it had navigation, which I've never had before.
Of course the interior is more upscale on the 15s, with more soft-touch, and a much more modern head-unit in any trim than the 4th Gen. The 5th Gen are a bit larger, and sit a bit higher....they raised the roof & seat position. One exception is the under cargo area storage, which shrunk in '15, it's now very shallow and doesn't hold as much as the 4th Gen. (Subaru, put the tire changing gear back into spare tire insert, and give us back the deeper storage space!)
On the road, they're pretty similar, although the 15 feels a bit more planted stock, with no modifications, with maybe a firmer ride than a 13/14. (10-12 had the softest suspension, they increased the spring/shock rates in 13, and then re-tuned in 15 again for the 5th gen. The 15s might be a bit quieter, I had limited seat time, and they were close. - But I'm comparing to a 3.6R, which does't make as much engine noise driving as the 2.5, so to my ears they were comparable. The 15 has a bit less road noise, but that could also be the tires. (I changed my tires in Dec of last year, and it made a profound difference). I've done the bigger swaybar and strut brace, which makes the 4th feel every bit as confident as the 5th Gen.
The engine/trans are the big changes. The FB25 went through some changes for the 15 MY, and it gained a couple of horses/tq over 13/14. Some 13/14 suffer from oil consumption issues, which don't appear to plague the 15+ models. The CVT was also reworked and mimics a traditional trans in all but WOT conditions, making far less engine noise accelerating, and a quieter interior during such maneuvers. For '15 even the 3.6R gets a CVT, the High-Torque version from the Forester XT. - Keep in mind there's the CVT extended warranty or campaign on the CVT through 15, if I was looking at a 5th Gen, I'd consider a '16, knowing it shouldn't be affected....and most likely has any other quirks introduced in '15 corrected.
I actually like my '12, as well as the design of the dash in the 4th Gen....maybe I'm an oddball, but I LIKE the faux brushed aluminum on the center console of the dash, with the vents flanking the head unit. My perfect Outback would be to transplant the electronics from a '17 into my '12....I also like the 3.6R/5-Speed combo, it's been used in much larger vehicles, so it should propel a 3600lbs Outback around as long as I keep her. (Same trans was in the Tribecca & used by Nissan/Infiniti in the Armada/QX80, shame it's dead as of '15 in the Outback).
I feel for your discussion, as I went through something very similar. For me it came down to, hey, it's better equipped and a bit less money, and really fast! - My wife wanted me to buy the '12 because it had navigation, which I've never had before.
That said, I was hit from behind, suffered $5000 of quarter panel and bumper damage, and as much as it sucks, that car is now damaged to me, even when it's fixed, so I'm looking elsewhere. I was really impressed by the '14 Ltd I drove a while back - seemed to handle so much tighter than mine, and have much better acceleration. 
