You would win the auction at $15.25 if no one else bid higher, even though you put in a manual snipe as well as an AS one. But you would still pay the AS .25¢ fee, since they placed a snipe for you and you won.
Had someone bid, say, $17.50, you would have won the auction for $17.75, and so forth, up to your max bid of $25, after which you would be outbid. It does not matter whether the bid was placed manually by you or by AS on your behalf. You have given AS your eBay ID and password, and authorized them to bid on your behalf. eBay has no way of knowing this; they receive the bid the same way, in either case.