There have been very few rumours about the iPhone 6s and iPhone 6s Plus but that is expected as both devices are likely to have the same form factor as the iPhone 6 and iPhone 6 Plus with minor internal changes.
There has been some speculation about the name of the next version of the iPhone. While most rumours suggest Apple will stick with the "S" naming pattern there are some rumours suggesting that Apple will call the next iPhone the iPhone 7.
According to rumors, the new devices will gain a faster A9 processor, 2GB of RAM, a 12-megapixel camera, an additional microphone to enhance voice quality, and potentially a new internal mechanical design to address some bending issues users experienced with the iPhone 6 and iPhone 6 Plus.
Several rumours have suggested the new iPhone 6s could incorporate the "Force Touch" capabilities first introduced with the Apple Watch, which is able to distinguish between a light tap and a harder press, enabling new gestures. Apple appears to be slowly adding Force Touch to its products, and recently, the company introduced both a 12-inch Retina MacBook and an updated 13-inch Retina MacBook Pro with Force Touch trackpads.
There are still rumours about Sapphire Display's being used in the iPhone 6s however there is little evidence to support these rumours.
The most significant upgrade is expected to come to the camera. While there are rumours of DSL quality images and 3D images coming to the iPhone 6s, we believe that the iPhone 6s camera will be a 12-megapixel camera upgraded from the current 8-megapixels.
The iPhone 6s and iPhone 6s Plus went into early production in late June. Production is expected to ramp up in July, so Apple is on track for a September launch.
9to5mac managed to obtain a rear shell of the iPhone 6s and so far there are some minor internal changes but nothing external.