Alton Brown swears on a stack of Cook Books that the fastest way to thaw something is to put it in a pan of ice water...
In the refrigerator: Thaw turkey in its unopened package on a platter to catch any defrosting juices that might come out. Allow one day for every four to five pounds of turkey. So, a 15 pound turkey would take three days to defrost.
In the sink: Put turkey breast side down, in its unopened package in a sink filled with cold water. Change the water every 30 minutes to keep the temperature cold. Allow 30 minutes for every pound of turkey. So, a 15 pound turkey would take 7 1/2 hours to defrost.