The 115% computed in the post is annualized return.
You will thus double the value of the account plus 15% so long as you can continue to successfully repeat the strategy every 3 or 4 months.
The problem with the strategy is that it limits your gains. If BAC were to rise above $10.50 by August, you don't benefit beyond that value. In essence is it actually a conservative approach but limiting.
If BAC were to rise to $20.50 by the 3rd Friday in August, you'd lose $10 of the gain, (but still have annualized gain of 115 percent). If for example, you bought today and sold for $20.50, you would have an astronomical annualized gain of about 462 percent.