Milage and age almost exactly the same as mine.
I'd say 42k is about right, but always nice if you can haggle a bit off.
15k is not a lot of miles IMO. A lower milage one will cost you more, so what you save on purchase price now you lose on sale price in the future.
It will look a fair amount, as some people buy a GT-R and then don't use it, so you do see very low mlage ones for sale.