I too went from the 6 to the 6s Plus. It's taking a bit of getting used to as I frequently have to use both hands when using it whereas I never did with the 6. Not to mention the sheer overall size of it when putting it in a pocket or finding a good place in the car to put it while driving can be challenging too. But the larger & higher res screen is a big improvement, plus when you also take into account the much larger battery as well as the OIS, I couldn't ever step back down to the 6s now.
Going from the A8 with 1GB of RAM to the A9 with 2GB of RAM, plus the additions of the new lightning fast Touch ID and 3D Touch, round everything out spectacularly too. Overall, this easily feels like the most significant "S generation" leap forward ever and it's just an amazing device in every way.