I followed HurricaneOf87's code and got to 14 of the 15 coins. My password is 6H25TTT.
The last coin is directly to the left of the starting area - I believe it's in the far left room, the one that has the chain leading upwards that goes nowhere.
Like HurricaneOf87 mentioned, that coin didn't appear to me when I passed through that room before, so there may be some kind of condition it needs to spawn. Hopefully it should be there and you can just pick it up and finish the game for us