Shelbi,
you're doing awesome! Just hang in there a bit longer. Yes it is "safe" to bring the chlorine levels up much higher than 15ppm ( although most people wouldn't want to swim in it..lol)
Keep it at 15+ a couple of days & continue with the filter changing & brush/vacuum (to waste). The filter socks are also excellent; stay on top of cleaning those as well.
after the algae is all gone you can let the chlorine levels dissapate back down to normal

Best of luck to you