You'll want to use the "max texture size" parameter to reduce the memory usage of your textures. Large geometries themselves are usually not the problem (except when the groups in OBJs are fragmented - see the link for a description and fix), but large textures with filtering enabled eat your RAM for breakfast. Disable texture filtering and turn down the "max texture size" to something in the 512-1024 range. If you experience blurry textures then, lowering the shading rate can help, but as a rule of thumb you shouldn't need to go lower than ~0.3. If the shading rate won't fix it, try larger textures, but be aware that twice the texture size means four times as much RAM usage.