I’m sorry, but I don’t think we have any strains with THC lower than 13%, and I’m not aware of any strains available anywhere at those levels.
You might want to look into commercial Hemp seeds. They are intentionally bred to have very low THC levels.
I’m not sure how you can harvest every 15 days, even the quickest autoflowers won’t do that from seed to harvest in that short of amount of time. You would have to develop some sort of perpetual grow, where plants that have been growing for a couple of months are getting ready to be ripe for harvest while others are growing in a vegetative season to replace the ones leaving the flowering season grow area. You will likely need numerous separated grow areas with different light cycle periods, especially if growing regular photo period plants and maybe even with autoflowering plants you will not be able to harvest the entire area every 15 days, even the quickest autoflowers are about a minimum of 60-70 days from seed to harvest.
As far as how many people, maybe Latewood would have a better idea as he’s had large agricultural greenhouse experience, I’ve never seen or been involved in any large commercial grows, only seen small one or two people medical grows.