Unfortunately there's no CLI option for the import at this time. There's no reason why it should take a long time regardless of board size, as all it's doing is reading the vbseo_config.xml file.
Is that file massively large for you for some reason? I don't recall the exact storage path but I think it's something like /vbseo/includes/xml/config_vbseo.xml
Do keep in mind that the more items per page you process, the higher chance you have of running afoul of the (default) 30 second execution limit in PHP - if you have display_errors turned off, you might think the process has just ended prematurely.