You can reduce the time taken to bake data and the size of the generated data if you bake your data into multiple scenes.
To predetermine the brightness of surfaces in your scenes, you can bake lightmaps. There are two ways to bake lightmaps for multiple scenes at once:
Shadows and GI light bounces work across all scenes, but the lightmaps and Realtime GI data loads and unloads separately for each scene. This means scenes don’t share and you can unload scenes with lightmaps safely. Scenes do share Light Probe data so all Light Probes for scenes baked together load at the same time.
You can bake occlusion culling data for multiple scenes at once to determine which GameObjects render: 1. Open the scenes that you want to bake. 2. Go to the Occlusion Culling window (Window > Rendering > Occlusion Culling). 3. Select the Bake button. 4. Save the baked scenes to make the scene-to-occlusion-data reference persistent.
This saves the occlusion culling data into a single asset called OcclusionCullingData.asset in a folder matching the name of the current active scene.
If you load a scene additively and it has the same occlusion data reference as the active scene, then the static renderers and portals that cull information for that scene initialize from the occlusion data. This means the occlusion system performs as if static renderers and portals are baked into a single scene.