How to compress pdf file generated by XeLaTeX?

I hope you can help me.
I am new to latex and perhaps I am not yet capable of creating well optimized code.
I am creating a file pdf full of figures and tables to send to my professor, who ask for a maximum file size of 500 KB.
I use OverLeaf and as a complier I used pdfLaTeX.
PdfLaTex generated me a file (about 60 pages) with a size of 1.5MB. With pdfsizeopt I’ve reached 647 KB.
XeLaTeX generates me the same file, but with a size of 1 MB. But with pdfsizeopt I have reached only 630 KB …
The images I use were created with MatLab in pdf. So they are in vector graphics. Maximum size 17-20 KB with a mean size of 2-3KB each.
My professor demands a file of 500 KB.
He gave no instructions on how to do it.
Would you guys know how to help me?
I do not know what to do.
thanks a lot