No. UWorld encompasses a World. Which when using World Composition will comprise of a number of sub levels (ULevel) for each cell of that world. If you require multiple worlds (Think different planets for example). Then you will have multiple maps set up with World Composition (each of these exist as a different UWorld when loaded) and each of these will have a number of sublevels (cells). You cannot level stream in a map that has World Composition ticked into another map that also has World Composition ticked, this is because they are seperate UWorld’s, they cannot exist together.