Slow printing via CUPS/Samba (large delay time) at Konica bizhub C220

Since January (maybe spectre kernel updates as trigger?) we suffer from large delay times when printing at our Konica bizhub C220 device (e.g. 1-2 html pages with one photo/image lasts about 3-4 minutes, other larger documents much longer).
In January we used older UCS 4.1 but since the update to UCS lastest 4.2 two weeks ago nothing really got better.
This week I tried one client to connect directly to the printer device without using CUPS/Samba printer share and noticed
much lower printer delay. It seems to be clear that using CUPS increases latency somewhat but with us the differences are enormous.

With CUPS we are using imported PPD from Konica (v10000.0001 for C360 series from, addressing it via ipp. At client side we use latest Win7_64 driver from Konica (v 3.7 for C360 series, both PS and PCL6 tried).

Since these long printing times are unacceptable, I have changed some frequent printing users to direct access for now. Since this is not a nice solution, I would be glad about any hint or tip.

Thanks in advance,