I've noticed Leslies always gives a range, and I believe it is over quoted (10-12 should be considered max 10, 12-15 should be considered max 12).
I actually have the speculation that what they quote as "12%-15%" in stock is actually 10% on the box. I've seen the site stating the 12-15 but the stores seem to never have anything over 10% when you have the box in-hand.
Generally, I can find the exact same product elsewhere for less. Leslies is notorious for being over priced. The one thing you can generally count on with them though is that they usually move enough product through their business accounts (pool cleaning companies) that I've never seen anything but "fresh" stock in store (don't have to worry about "last season's chlorine").
Arizona, Fountain Hills: Ace Hardware - $6.99 for 2 gallons of 10% (about $0.27 per oz. Sodium Hypochlorite)
- less than 4 months old by manufacture date
- stored indoors and air conditioned