I believe your processor should be warmer than that. 15 degrees C is fairly cool, especially if you are having days warmer than that.
As for the fan, I've just fired up my C2D for the first time and the fan didn't spin until the processor warmed up a little, then it was spinning on and off as the PC did things, now it's spinning continuously while the drive formats.
The intel fan on my other computer (Celeron D) has just always spun full speed.