The 15" has the butterfly keyboard which does break really often. Some people went through 3 keyboards in a year, for others it didn't break. If only 1 key breaks you need a new top cover, new batteries (glued in) and a new keyboard. That costs 'a lot'. there was an extended warranty for those keyboards, but that is the past.
Further more both do totally overheat if you connect an external monitor to it. I had one from work, that slowed down until it throttled the cpu back to 800mhz ... It was utterly slow. When i had to compute something I disconnected the displays, hit the button and then connected the screens again. Saved me 10+ minutes in the summer ... ridiculous design flaw.
I would stay away, far away, from both models and do yourself a favour, buy a new mac. Even a macbook air is faster than those 'pro' models.