Why adding a static mesh for the foliage is so slow?

I’m using the Open World Demo Collection package from the Marketplace.
I noticed that when I drag and drop a static mesh into the foliage tool, it takes too time to load!
Moreover, if I add very few trees the building lighting compiling time is absolutely not reasonable…it takes minutes. Could you imagine for a normal open world game? Seems to be that the compiling time grows exponentially as I add trees.
Is it normal? Am I doing something wrong?

Same problem with me, Just some static mesh will have the problem, I try to use another static mesh, the speed is ok

The open world demo collection is VERY intensive on systems, which is most likely causing the issues you’re experiencing. I experience the same problem on my system when I import the rocks for the first time in a new project. Many others also experience this. It can freeze for several minutes at a time. This is why the assets included look so nice! You can try adjusting their settings manually, but you’ll have to accept the slow speed when opening them, unfortunately. It typically only takes some time when you first open them, especially if you have a decent setup.