I doubt a 3 year old new golf GTi will be £15k more like £20k
I got mine at 4 years old for £13.8K , 3 door , white , 18s (mint and refurbed) , leather , 18500 miles , 2 services and MOTs free , cambelt and waterpump done , 12 months warranty and 6 months tax , from a VW Dealer. Fair enough it was an old shape by then , but Im not sure GTIs hold their value as much as they used to.