My 150-200 page returns are still about 5-6 MB after I print in Lacerte.

You can compress them locally using the "full" version of Adobe Acrobat (not the free Reader) and they will get down to 500-600k (see my improvement suggestion here).  But you will need to manually input the new, compressed file into DocuSign.

I'd call Support and see if there's a reason your files are so large.