You sure those youtube vids confirms the unknown song is track 15? Maybe somebody assumed.
From JP sites:
- trial: get Kunlun ending
- sound test: get S in trial
- museum: get GOOD ending
Good end: Fukenshi questions all YES, Kei question YES, Lisbon question YES, beat all Hakke, don't beat any Fukenshi
(there may be other conditions, here is flowchart in moon, you want FIN):
http://blueviolet.ninja-web.net/game/maken/stage.htm
The comment is saying that, yes.