Since the switch to 64-bit code and hardware, I have not been very impressed with iOS 11 or 12 and, currently, I have not installed either on my 2015 iPad Pro.
My iPad Pro has been working and performing just fine with iOS 10.3.3.
I have been missing out on some significant application updates, but have decided to forfeit these, for now, for stable operational performance of my expensive iPad Pro.
iOS 11 was a mess, IMHO and avoided it completely
iOS 12 has some intermittent touch response issues reported across all years and model iPad Pros from users here and even some reports of this intermittent touch responses issue affecting 5th and 6th gen 9.7 inch screen iPads, as well.
Still some WiFi and Bluetooth connectivity issues, as well, in iOS 12.
Since upgrading iOS is a one-way affair, I am going to wait out the entire iOS 12 update cycle until I make a decision whether to upgrade, or not.
Best of Luck to You!