A report from an inside source in Greece stated that the iPhone 6s will be announced September 8th, 2015. Emails sent within the telecom company, Vodafone, reveal that the iPhone 6s will be available for pre-order on September 18th, 2015. They go on to divulge that the iPhone 6s will officially begin shipping to customers on September 25th, 2015.
The source has proven to be reliable, as Vodafone was the culprit for the iPhone 6 release date leak. Almost a year ago, a Vodafone employee leaked information stating that the iPhone 6 was to be released on September 19th, 2014 which proved to be 100% true.
More iPhone 6s leaks here.