In my opinion, iOS 11 is absolutely dreadful on the Mini 2 even if you turn a bunch of features off. Not one animation renders properly while going through the operating system. The new features of 11 don't even benefit the 2 that much so there's not much reason to update.
The Mini 2 was a great product pre-iOS 9 but once that update came it killed the device. It's only getting worse with more updates, so I would stay on the earliest firmware you can until you can upgrade.
Hope I helped - sorry to be the bearer of bad news lol.