That's rotten luck mate, with this weather it's so easy to do so don't beat yourself up too much. That's a lot of damage for 15mph though? When I got rear ended at about 40mph and shoved into the car in front I had nowhere near that much damage so you've been quite unlucky.
2002 '02' IS200 SE Auto - DVD Satnav with Voice Activation - [COLOR="Blue"]Strathcaron Blue - Parking Sensors - 5000K HIDs with Anti-Glare Bulbs - PIAA 6500K Main Beams - LED Sidelights - Mirror/Sunroof Closure - TTE Styling Kit - 18" Styling Kit Alloys with nitrogen filled Goodyear Eagle F1 Asymmetric Tyres - Bluetouch Multimedia Kit - Gromaudio AUX in - Black painted calipers with silver Lexus decals - 12 LED Dome Light - 96 LED Boot Light - Stainless Steel Sport Sill Plates - PIAA Silicone Wipers[/COLOR]