190k does sound like you would have to remove a lot, when you build, put your logic and devices in at the start, use prefab galleries to “load” the level in advance to approximate weight before you spend time building.
Also, reducing loading range under streaming settings will reduce the amount loaded at any time.
Run tools/audit/statistics to get a calculation you can sort per undivided or total actors to determine which are causing most impact.
Observe any extremely long landscape splines or attached/parented actors that may be combining and loading in entirety regardless of streamed grids.
You’re doing good work keep it up