Not sure about the $15k part. WE just bought the lease on our 2008 M3 after 45k miles. Loaded for $38k. Most were in the $40-$48k listed price. Unless you could get it CPOd, which I don't think so ater 50k miles, then I'd pass. Repairs can get very expensive on these things and you have no idea how well the previous onwer took care of it. We had a prety good idea on ours, which is the main reason we kept it.
Find one the dealer will CPO and give you the 100k miles warranty on
And, the M3 is more than a badge. Totally different feel to that than my 335xi. Way more fun to drive.