Yes, the bleachcalc (which i wrote ) will tell you how much bleach you need to add to strike a particular ppm. Just enter your bleach strength in whole numbers (i.e. 6% = 6) and your pool size. Enter 15 for ppm desired, and read off how much bleach to dump in. When you test next time, if you are at say 3 ppm and want to get back to 15, enter the difference (12) and away you go.

Michael