The #15 hasn't operated for the past couple of seasons now on the YMSPRR. I believe she's in need of some significant work, and won't be in operation this season, either. If I remember, the last real rebuilding needed to be done on her was at the WS&CV, before moving to Fish Camp. If I remember, one of the guys that did it worked from Frank Cottle for a time. Jeff Badger will be able to tell you more on the 15, as whatever I heard was second-hand.
I was down there in '96 and was extremely impressed. The enginehouse doors are left open; visitors can easily catch a glimpse of the 15 through the door. The Stauffer family has operated the line since its construction in the late 60s. I saw the #10 run myself; the 6-chime whistle on her (and a fine one at that) came off one of the SP's P-4 Pacifics; one of which (2410) served the 2-1/2 mile branch from Vasona Junction to Los Gatos which was once part of the SPC's narrow-gauge mainline to Santa Cruz. The whistle was I guess presented to Vic Shattock, founder of the Golden Gate Live Steamers, which today lies in the shadow of Erich Thomsen's 5" scale narrow-gauge RVRy in Berkeley.
-Ed Kelley