As of August 2015, no release date has been confirmed for the iPhone 7. The iPhone 6S is likely to be Apple's next release; rumors are that it is likely to be released sometime in September 2015.
In the various photos and videos that have surfaced online, the iPhone 6S appears to be nearly identical to the iPhone 6. This supports Apple's previous tactic of focusing on improving the hardware rather than the physical appearance of the phone when transitioning to the S-series iPhones. With the looming release of the iPhone 6S, it appears the iPhone 7 may have to wait until 2016.