With the 6S, also came the new 6S Plus. It was announced and launched back in October 2015 and is the successor to Apple’s first phablet iPhone 6 Plus. Like the iPhone 6S, the Plus also gets much improved hardware and also one of the most notable features which is 3D Touch. The iPhone 6 Plus was a very powerful device in terms of applications and camera performance, among other things, and the 6S Plus attempts to even improve on its predecessor.
3D Touch adds two more touch controls to the iPhone. In addition to a standard press, there's a harder press call 'Peek' which allows to preview items such as messages, photos, etc. without fully opening them. If you decide to open the previewed item, you can press even harder to 'Pop' the item into its proper view. It is used in stock apps, and is being slowly incorporated into third-party apps.
The camera has received a nice bump. It has a 12 megapixel sensor that takes more detailed photos, and allows for 4K video recording. Slow-mo videos can now be recorded at Full HD 1080p 240fps instead of HD 720p 240fps on the iPhone 6 Plus. Another neat feature called 'Live Photos' captures 1.5 seconds of video before and after your still image, which gives you greater context of every photo you take.
The faster processor (Apple A9 chip) is also more efficient, resulting in a slight increase in battery life. It comes with the M9 motion coprocessor that allows you to use "Hey Siri" feature without charging the phone. Touch ID has also received a boost, and is now twice as fast.
The iPhone 6S Plus is also water-resistant. Apple hasn't marketed this feature, but several tests suggest it can be submerged in shallow water for short periods of time without any damage. It isn't recommended you do this on purpose, but it is still nice to know it can take the accidental water spill!
All in all, the iPhone 6S Plus is a great improvement over the previous iPhone in every single way. It makes for an altogether smoother user experience that is recommended for every iPhone user who can afford to upgrade.