well if you set it to 'render'... it's going to complete a whole rendering for every viewport that is set to render, every time you plot... for every viewport.... so yea, it'll take some time. best bet is, if you want a RENDERED image, render it to a file, and save it... then if necessary, import it into the DWG.
if it's just for a visual style then yea, viewport suffices.
Very odd that scale-lineweights would effect it in such a way, I've never come across that.