Let’s say a game has 50 levels. Each level has the exact same 2000 x 2000 static mesh floor common, as well as the same lighting. The only things different in each level are the placement of walls on this common floor, and the enemies spawned. These levels are also independent from each other. In other words, they are not connected. As a player, you finish Level 1, and Level 2 loads.
With these in mind…
Would you create the common mesh floor in the persistent level?
OR would you add the mesh floor in each of the 50 streaming levels, and make the floor coordinate the same X,Y?
Assuming that you indeed have one floor but swap assets and lighting you could essentially keep the mesh floor as the initial level loaded and persistent to your master level.
Then create a new level using that base using the levels tab and setting it visible - add in your meshing and lighting and blueprint to the new level you made and just stream it to overlay to the master containing your mesh floor.
you may want to space each level out more so however depending on workflow IE your master with the mesh floor a level with the meshing and lighting and a level with blueprint for each of the levels streaming onto your master.