Rim clearance isn't really the issue. Tyre size is.
150 offset is +25. Legally maximum track increase is 25mm. This means that you can reduce your offset by half that = 12.5mm. So it means that leagally, you can go down to +12.5mm offset.
You can go out to +15 mm (GX standard offset) less 12.5 mm (rules maximum) and you comply with the rules. This will allow you to go to +2.5 mm offset legally.
+10 mm offset keeps the tread just inside the mudguards.
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