I usually am one to LOVE the iPad mini. I remember in 2012 when I first held an iPad mini, I had never had an iPad of my own, and I wanted that to be mine. Luckily, I did not get it because the iPad mini 1 has such a garbage screen and is really slow now. But yeah, I ended up getting a mini 2, and I really enjoy the size. And that it is just a shrunken iPad air, same specs!
But for you, definitely get an air 2. Not only because you already have a large 6 plus, but because the iPad air 2 is considerably faster, and will be more future proof. The mini 3 is last years iPad mini with Touch ID. Still has the A7 chip and everything, so I consider the mini 3 essentially a waste of money.