While you COULD use a good dose of PolyQuat, I have to disagree with Michael on one thing:

Without knowing your CYA we cannot know if an FC of 15 should be effective or not.

If you have a CYA of 100, you need to keep FC at 25ppm. 15 won't be successful. However, if your CYA is 30, then FC=15 should be effective.

Also, a caveat: When you dose your pool with PolyQuat, your FC will fall DRAMATICALLY. You will need to get it back up. I don't know the chemistry, but PolyQuat does depress FC, and lots of PolyQuat can really push it down.