My map is too big and the memory will overflow, can I let the Houdini engine bake the sub-levels and export them?

Yes, you need World composition turned on in UE4, and then you can add attributes to your landscape tiles in Houdini to have the HDA save the tiles to separate levels when you bake the asset in Unreal.

Docs here:
https://www.sidefx.com/docs/unreal/_landscapes.html#LandscapeWorldComposition [www.sidefx.com]

Tutorial here:
https://www.youtube.com/playlist?list=PLXNFA1EysfYnrFeCn4NYgCq3stsBWLnpB [www.youtube.com]

FYI In UE5 world composition is depreciated and replaced with World Partition, not sure what the Houdini to Unreal workflow will be moving forward.