Hi, I would like to plumb in my compressor using 15mm copper pipe but don't know how to tail it off to 1/4" bsp and also connect the pipe to an air filter.
Yes, that's how I've done it, 15mm to 1/2" bsp male or female, then adapters.
My regulator is 1/2" female so nice and easy there.
Thinking about it, I come straight out of the bung in the end of the tank to a 1/2" ball valve, then a flexible hose with 1/2" fittings crimped on each end to stop vibration issues, then 1/2" to 15mm compression fitting, so I don't even need adapters for that part.
as madkayaker says, you will find a selection of 15mm compression X 1/2" brass fittings --standard plumbing stuff, either with a male tale or a female tale, then reduce from 1/2" to 1/4" ( remember, handbasin/kitchen sink= 1/2" Bath taps 3/4") + of course other fittings-push fit and solder for 15mm as well