From your figures I make it 12.5 kWh/sq.m., so yes, less than 15.0 = passivhaus! The electricity price is quite expensive there then: £450 for 1316 kWh is approx 35p per kWh but still £450 p.a. is still hugely different to the bill for an average house in the UK.
I hadn't thought much about volume as opposed to floor area (I'm just an enthusiastic amateur, not an engineer!). Does having high ceilings make a significant difference to heating costs?