I have only been able to update the ipad mini 2 for ios 12.1.1. I don’t know whether this would make a huge difference or not.
I have launched a flight on causal from Toronto to Stansted now, which is at least 6 hours.
I have not reinstalled the app, just cleared all the running apps from the background and cleared scenery cache in IF’s settings. I have around 1-1.5 GB free storage space as well.
My current graphics settings are: everything on medium, live airplane count medium, AA off, frame limiter on, automatic low power mode enabled. Brightness reduced all the way down, connected to WiFi only and the ipad is also on charger.
I will get back to you at least free hours from now.