A3015 - Altimeter 30.15 inches...
SLP - Sea Level Pressure (212 is an encode for millibars, but I can't remember how to decode it!)
AUTO - auto observation.
The slightly odd thing about this Metar is that everything after the Altimeter setting (A3015) appears to be in the American format - Fairford is an RAF base right (and not a USAF? - sorry for the ignorance!)?