The difference between 1.5mm2 and 2.5mm2 over 10m is 5.2V vs 2.86V drop.
A 36W loss difference ; over one hour charge you would have lost 36Wh, assuming 24c/kWh that’s 0.9c per hour: basically bugger all.
Heavy duty doesn’t describe the wiring; it describes the insulation around it. It’s...