When I am using Open world demo and try to add a tree to a landscape unreal is literally locked up. I am using an I7 with 16 gigs. I know there are a lot of textures and materials in OWD, but this is ridiculous. Also when load the Kite map and run it also locks up unreal.
I am having the same problem and I found an explanation in this post:
At the bottom of the page, Eric Ketchum (staff), says you need a very very good machine to make it make OR scale down the textures (from 8k to 2048*2048). It looks like a super high res problem.
Hope that helps.