Reducing page size by 50% while maintaining ratios

I wasn't able to figure out how to easily resize the pages (it's over 20 pages, so I was trying to avoid doing it manually), but saving it out as a print pdf and reducing the image qulaity helped bump it down to 8 MB. I originally saved it as an interractive pdf becuase it has interractive elements, but I was able to preserve those (just hyperlinks) in the saved for print version. 

Why are you creating an interactive PDF? What if you export as Print PDF and then reduce the file size in Acrobat?

How many pages is it? You could create a new ID document at the right size and then place and scale the PDF that way then export a new one.

Can you manually select entire spreads and use the Scale Tool to reduce them to 50% of size and then change your page size to 8.5 x 5.5 and place the reduced files accordingly on the reduced pages? I know that sounds tedious but it should work.

By the way my experience with emailing pdfs has been that 24 mb is usually the upper limit for emailing. In that case your 23 mb files should already be OK.