Hello Jim, can't be much help here but would love to find a simple solution...
I've ran into the same problem repeatably, mostly by limitations of my CAD system (Pro-E). If I change the fonts, it sometimes reduces the file size, but then puts detail #'s outside the detail balloons...
I posted a drawing awhile back, & our esteemed mod/admin Jo took a screen capture of it with some pretty good results (Yielding in a smaller file size with not much degradation...)
Apologies for not being more helpful. I'm looking forward to additional responses so thanks for posting this, we're coming into engine design season (After summer activities cease & we're chased indoors a little more.)
Looking forward to any goodies you post...
John