[cups] Kyocera FS-C5300DN (KPDL) very very slow

[Gandalf Corvotempesta]

Hi to all.
I'm trying to use a Kyocera FS-C5300DN (KPDL) printer with Ubuntu
Ubuntu 16.04.4 LTS / CUPS 2.1.3 but PDF printing is very very very
slow.

Even by trying to print a 67kb PDF, the resulting PS file generated by
"gs" is 4.2MB and take about 10 seconds to be generated.

When printing a 300 pages PDF (3MB in size), about 10 seconds are
needed between each page (and many minutes before printing will start)

How can I speed-up this ? By using foomatic PPDs printing is very very
fast, but print quality is low, black is printed as a light-gray.

Any idea ?