Well it should take about 30 seconds, is the scuba tank full?

Thanks for your reply - yes, the Scuba Tank was just filled and shows 4500psi on the fill gauge.
New gun and never owned a PCP before, so wasn’t sure what to expect (and didn’t want to risk damage to seals / valves etc) - but I guessed about 30sec should be about right - not 15 minutes !
Thought firstly that there was a problem with the PCP and checking said if air was coming out of the Scuba airline at HP and a hand pump was pushing out air past the filter, then it must be the gun itself or the fill probe.
“Bit the bullet” and started checking things in sequence - pulled the Foster fitting off the probe and found 2 nylon seals had been fitted and screwed up so tight that the centre hole had been squashed almost closed and one seal had been forced, cone shape, up right into the probe itself, effectively almost completely closing the airway.
Removed these seals and fitted a new SINGLE seal, nipping the Foster / Fill probe up tight - now the gun fills in very quick time and I can even fill with the hand pump without passing out !