On my MSI Laptop having it plugged in the original Power Supply was crucial. Neither the replacements nor a docking were sufficient. Besides I activate Gaming Mode and have performance power ACPI activated. Newest drivers are sensible. And DO choose the right GPU in Nvidia Settings. The Iris is probably the power-save GPU on the motherboard. For battery life reasons this one is selected preferrably and you have to switch the settings for Unreal Engine.