I have a HUGE PLUS ONE for this problem. After the update, it seems as though PS doesn't compress the file down like it used to. I presume you haven't found a solution for this yet?
Have you tried a 3rd party program that produces .pdf's and installs like a printer? There are many like CutePDF, free.
In Ps, "print" to the pdf printer instead of export
The issue is that something which once worked no longer does. The answer to a bug isn't really "did you try this workaround"...no offense, of course. I could certainly export each page as a PDF, then run it through a compressor or something. But this thread is about a bug in the export feature that (in my case) didn't exist until the most recent up date.
Found a solution to this problem:
• Take the Artboard PDF you exported and open it in Photoshop.
• Save as a PDF again
• This time use the "Photoshop PDF" option under Save As.
Unfortunately it's an added step... but at least you can get a compressed pdf.