How much time would it take those 15-20 cars to get through the intersection? If quick (couple of seconds per car) I would probably wait in the queue. Otherwise I would filter up as described by the others and turn left with the lead car. Strategy really depends a lot on the cars. If you are waiting in line and the cars to your rear behave impatiently (because you are in front of them), I would avoid waiting in line. If you filter up and after your turn are met with signs of displeasure because you "cheated" then you may want to wait in line. Try it both ways for a while. Experience will guide you. An option is to turn right, go down a ways and then make a U-turn. None of the drivers that saw you turn right will be there when you return and so you won't "offend" anyone.

Also, 5 minutes can make a big difference in traffic so adjusting your schedule can help.

Good luck. Report back please.