As far as casing and appearance go, the iPhone 6 Plus & 6s Plus appear very similar. The “S” logo on the back of the iPhone 6s Plus is the mark that lets you know which model you have. But aside from that, it can be a bit tricky to tell the difference between the two devices. However in terms of performance the 6s Plus was a significant update. The upgrades include, 3D touch, a better camera, live photos, faster processor and more RAM. The iPhone 6s Plus also introduced the rose gold color option. 3D touch on the 6s Plus means that you can navigate differently since this model can distinguish between a hard press, a light press and a tap. Video recording on the iPhone 6 Plus is in 1080p and the iPhone 6s Plus made the jump to 4k.
In terms of battery life the original capacity on a new phone was estimated to be approximately the same on both of the models.