If it has only one 12v rail with 15A then it must be pretty ancient... I ran my 8800 GTS for a while on my ol Seasonic 400W with one rail and 18A on it, but 15A might be pushing it, especially if it were/is a non-name PSU.
This Seasonic will do for now if you're coupling this with a Core 2 Duo with maybe 2 HDs and a soundcard; but I'd get a 430W one so you won't have to upgrade your PSU on your next upgrade again. The 430W is somewhat more expensive though.
330W:
http://www.newegg.com/Product/...x?Item=N82E16817151021
And for those saying 330W is not enough, I actually tested my rig with a Watt meter and power consumption under load has never been higher than 210W, while the Seasonic with an 80+% efficiency should do 264W, which is enough to spare.