You may need to use a service like Adobe's "Send Now", store the file on a web site and sent the link, or split the file into 2 sections and send each section as an individualt email.
Many email services restrict the size of attachments so as not to overwhelm the internet connections with massive amounts of data.
Some PDF files because of the content cannot be compressed any more.
With Acrobat Professional you would have the Optimizer feature and the ability to select the compression and font embedding that can affect the size of the PDF. You can also see how some of those changes affect the size of the PDF with the Audit tool.
Acrobat Professional is available as a 30 day free trial product.