If you can consistently keep it around 15, it will clear. Try and take a net and see if you can scoop any debris out. It would be great if you could get someone to add some bleach twice a day, but if not, then just hit it hard when you return. It really is important to hit it at least twice a day with bleach. It will clear if you can maintain this sustained high cl level.

Have you taken a look at the thread right above this one called "Skeptical that Bleach will Kill Algae?" If not, take a look. The pictures are pretty awesome.