According to Phil Kompass, it's always runnable but 15 might be pushing it. In comparison, the Rouge is still fun at 14 m^3/s. The Petawawa gets 'creekier' at lower levels, new lines and eddy hoping etc. Railroad rapid might be quite dry. In my experience, the lowest I've run it was at 40 m^3/s. Railroad rapid was quite tricky, and we all walked Lovers because it looked nasty (in fact we ran the left channel slide). But the right channel of Suicide was a nice drop. You might like it, but try to do two laps to make it worth it... If you go, let us know how it went!
--C.