Hi,
you are using OS X's built-in print-to-PDF functionality I think, right?
PDF in itself is a complex format, so some growth in size over the sum of the original file sizes is quite understandable.
However, you can set DPI inside the Photo Mechanic's Print dialog. The DPI value will have a huge effect on the resulting PDF size, so if you want only a PDF for emailing and viewing on screen, by all means set a lower DPI like 72 or 96 or what your target operating system's screen resolution is.