Currently, the favicon.ico contains sizes 16, 32, 48, 64, 128 and 256, adding up to a file size of 361 kByte.
favicon.ico is only required for IE <= 11, modern browsers understand PNG and SVG. An SVG is even already linked from the pages.
For any legacy browsers, a favicon.ico containing sizes 16 and 32 should be sufficient.
BTW, KIO even aborts when trying to use the favicon: "Icon file too big, download aborted" (err=KIO::ERR_SLAVE_DEFINED)