If you consider that the average driver drives around 12-15k miles a year, the milage in 4 years is 48k-60k. You are not that far off from the 15k per year number. If you like it, and it has been well maintained, then go for it. Don't let that little extra milage discourage you. Hell, I almost consider the first 50k miles just breaking in for the 3.0/3.3L Nissan V6s!