Any loss from PDF to PS level 3

If PDF converted to PS with level 3, is there any quality loss? I did a expreiment below, I convert PDF (with smalles file size setting) file to PS level 3 and then convert the PS back to PDF (with smalles file size setting), to my suprised, the file size doubled.

I do not know what is happening in PDF to PS level 3, I am wondering is there any quality change in this process, such as image and font resoluation and so on.

Thanks for your help.