I ported my custom PDF Export script from Bridge 12 to Bridge 13+ and just setup a template because I produce PDFs for work, and I'm seeing pretty close to identical filesizes with the same set of photos. Make sure your settings haven't changed from what you have been using with the older Bridge version. Adobe changed the template XML format used to store each template's settings but that shouldn't have any effect on the finished product. My last output used 413 1600 pixel wide JPEG files, 96ppi, quality 3, plus a small header graphic, and came out to 15.24MB. This is consistent, the one with almost the same set of images was 16MB from Bridge 12.
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