It was 15 years from the time that I won the Pegasus Award for "The Wind From Rainbow's End" until daisy_knotwise and I won for "My Husband, the Filker". That seemed like a long time.
It turns out though that there's exactly one filker who has gone longer between winning Pegasus Awards.
(And clicking on every name to discover this was an interesting process. There've been a great many fine songs nominated over the years that have never won -- and some that have sort of faded away...)