First thing to try is to simply do a Save As under a new name. That forces an optimization of the file and can reduce its size by a lot. If that doesn't work you can try File - Save As Other - Optimized PDF.
If you are a subscriber or owner of Acrobat DC, then it can help you reducing the size of the file. Acrobat reduces the size of a PDF file without compromising quality.
The Acrobat PDF compression tool balances an optimized file size against the expected quality of images, fonts, and other file content.
No, I’m only an owner of Acrobat XI. I have limited needs of Acrobat and until now, I haven’t found anything that XI couldn’t do. I’m still hopeful that if XI can’t do what I want, I’ll find some other way to get along.
Adobe Acrobat XI is an old and EOL application. Adobe strongly recommends that you upgrade to the latest versions of Adobe Acrobat DC and Adobe Acrobat Reader DC. By upgrading installations to the latest versions, you benefit from the latest functional enhancements and improved security measures.