I’ve spent 8 years in architecture and every round of job applications I’ve learnt new tricks to reduce the pdf size while maintaining the pdf as a vector and not rasterizing it. There are many ways or methods you could be doing or using wrong for me to help you figure out how to reduce your portfolio size. But let me start with the most major thing you might be doing wrong (probably aren’t) which is using any other software except indesign to make your portfolio. Next comes the types of “links” in your indesign and then fix your output settings on your export window. With the right settings I always have a portfolio that is lesser than 10mb and a further smaller version lesser than 5mb while maintaining decent quality. My portfolio is actually considerably long and has 10 projects on a minimum and 60 pages. I can share exact details without rambling on here if you’d like to connect.

I would try to review the graphical content and be conscious about what you are trying to show for a project. One more thing that I recommend to go through is the hygiene of your vector files. Sometimes the quantity of lines and other vector information significantly bloats the file size, so in these cases maybe you want to consider rasterizing them to a higher quality jpg. Hope it helps!

Google search how to compress PDF, you will find some website that can compress it

Find away around the system. Use an instant free transfer site like wetransfer.com and send them a link so you don’t have to spend hours breaking it into tiny pieces or reducing image quality.