It should be fine...HOWEVER, turning it on before it's completely warmed up again would be a bad idea. Cold doesn't hurt electronics, in my experience...but turning them on when they've been cold and condensation has built up can be bad.
So...basically it's OK IF you'll have time to let it warm up again before using.
Though Rose may have another opinion, I don't know. ;-) We deal with a lot of cold laptops up here, though!
Let me preface this by saying that you're asking a San Antonio girl what 15degreees is like.
<pondering that for a moment>
All righty, then! ...
How cold will it get in the car? Will the sun be shining? If so, tuck the machine somewhere out of the direct sunlight. If the sun isn't going to be out, then I wouldn't leave it in the car. Keep the machine above 32degrees if at all possible.
Just pack it with you ... it's a portable ... <grin>