How can it be that it is 23 but it feels 15 degrees cooler right now?

Wind Chill: the effect of the wind on the human body, extracting heat from it by removing the thin layer of warm air that would otherwise surround you. 

The real air temperature is still that quoted - the 23º in this case - and that would be also the temperature of exposed, inert surfaces once they have stabilised to the air temperature.