There is a mathematical calculation to figure out how much chlorine the T15 can produce in a given amount of time...but I try not to make it that complicated for me. I would manually dose the FC up to 6 with liquid bleach.
My pool is 14,000 gallons and I run my pump for 5 hours at 25-30% - CYA is 70-80. Assuming I lose 2-3 FC due to sunlight daily. These are the variables you need to consider. The CYA is important because if it is lower, sunlight will burn more FC - and this does have a significant impact on the run time in conjunction with % that you will need to maintain that FC6-7.
You are really going to have to see what works with your pool based on your water balances. So I recommend a liquid dose to 6, run the pump for whatever you feel keeps your pool clear of debris. If you are comfortable with 5-6 hours, then I would probably set it at 50% and measure at the end of day to see where FC landed. If it lands at 5 (dose back to 6 with liquid) and turn it up 10%. Then see what happens the next day.
If it lands at 7 that first day, I would leave the FC at 7, dial down 10% and see what happens next day - remember you start at 7, so if it ends at 6 the next you need to increase it some, say 5%.
I hope the explanation makes sense