I have a 2017 iPad Pro 12.9 and for normal tasks, it's not really noticeably faster than the Air 2.Ya you’ll be fine to hold out. Just don’t use an iPP that way you won’t know what you’re missing. My Air 2 did everything quite well until I upgraded and then I thought wow, I can’t believe how fast I thought my Air 2 was
That said, the lack of ProMotion on older models did make my other devices (iPhone 7, Pro 9.7, Air 2) feel a bit laggier so I've disabled that feature on my Pro.