I you didn’t do it yet, I highly recomend activate “World Partition” on your Islands. This will help a lot with the memory usage.
This feature automatically divides the world into a grid, and streams only the necessary cells. You can manage the general cell size and the streaming radius.
In addition, you can set FALSE the option “Is Spatially Loaded” on every asset you want to be always loaded even when “World Partition” is enabled.