Frage Cutting PA6 and PA4 alluminium - 2,2kW machine

Hello,

I would like to ask you for help.
I'm using 2,2kW machine Megaplot XMD 32 : www.megaplot.com.pl/index.php?id=426
Endmills: HSS DIN 327-B - 4, 5, 8 mm
Materials: PA 4 and PA 6 alluminium.

I found tone of informations about parameters on internet, but settening range is so big, that I still have no idea how to set them correctly.
With current settenings ( 2300 mm/min, 0,4mm deep and 21 000 rpm) i'm killing endmills definitly too fast. When I slowed down and gave bigger cutting depth then machine got terrible vibration.

Any suggestion or advice how to calculate correct parameters? I'll be very greatfull for any help:)
Regards
B.

One more thing - material got 10-15 mm thickness.