Adobe PDF file too big to upload. What are my options?

I have 4 Illustrator (Adobe pdf) files I need to upload to a freelance website for a job I did. I saved each one as a PDF file but they are 184 MB each. The site only accepts files under 100 MB. Each file is 36 in X 24 in and 300 ppi. That's the size they need it printed at for a poster. Each consists of 1 large image for the background, a woman cut out in photoshop, and some text in "thought bubbles." What are my options to be able to upload them? I searched on here for duplicate questions but didn't see the same issue. Originally I had them done in Photoshop at 600dpi but cut in half at 18x12 in. but they were still around 126 MB. Someone here mentioned it would be better in AI. Thanks for your help.