Try then to transcode from Pr with Multiplexer set to None. You'll get separate audio and video files. You'll have to create a new timeline in En and add the audio and video files from Pr to it and re-create any chapter points you've done. Be sure to delete your old timeline in En after. As for export settings in Pr, use a bit rate calculator to figure your max bit rate. Be sure to allow for video assets used in any menus you have planned for En.
The reason I'm suggesting all this is because after disc space, I suspect audio as the next likely culprit.
Here's a good bit rate calculator: DVD-HQ Bitrate & GOP calculator © Rui del-Negro 2005
Jeff