One person suggested using an external tool (I was trying to find a MATLAB setting).
I found the following Bash command worked amazing (form 3007 kB to 277 kB):
- gs -sDEVICE=pdfwrite -dCompatibilityLevel=1.4 -dPDFSETTINGS=/screen -dNOPAUSE -dQUIET -dBATCH -sOutputFile=output_small.pdf input_large.pdf
The image quality drops substantially, but the text and text colors all look great. The figures are still good enough, and a file size reduction factor of 10 is impressive. This is exactly what I needed.