IPhone 6 will be dropped before the Air 2... I think it will receive iOS 11,12,13,14 and maybe 15
It has 2gb of ram , and performance it's nearly indentical to iPhone 6S/SE . My guess that it will be supported until 2020 or 2021..
I will be in the market for a new iPad in 2020. The iPad Air 2 will be the new iPad 2 . If the iPad 2 runs iOS 9 , I think iPad Air 2 can run iOS 15. Hahahaha