The rules are not set in stone but they do work in that the best solvers cannot dominate the game and play clue 'ping-pong'. In practice it does not take very long to reach an 'open'. If a majority want a rule change it's not for me to say otherwise but I'd be very wary.
I think that 15 minutes to "open" is a good balance - until the end of the game looms, when it should be quicker, but that's within the setter's option anyway.