The reason I ask about the length of your beer lines is that there is a balance between line length, line diameter, and serving pressure.
I personally use 10 foot long (3 meters) lines that are 3/16" (4.75mm) inside diameter, and serve at 10-12 PSI. This gives me the carbonation level that I like, without too much foam when pouring. The length of line, combined with the small diameter, actually reduce the pressure and the flow rate at the tap. A larger diameter line would need to be longer to achieve the same result. I think that the folks that get metric sized tubing use 4mm ID beer line, or maybe 5mm, I'm not sure. There is a chart for this somewhere, google may help you with that
Please correct me if I am wrong metric folks!