1.5mm is utterly inadequate for mains separation unless you have a proper conformal coating which
is unlikely. Start with more like 10mm, and consider using cutouts too. The kind of spike voltages that
occur on mains wiring when fluorescent lights or motors switch on and off and during thunderstorms
are measured in kilovolts. Its a great idea to incorporate a transient suppressor (MOV) to help prevent
destructive spikes in mains PSUs.
MOT? ministry of transport?