iPhone 7 is water resistant, while the 6s is not. The iPhone 7 can withstand submersion in water for 30 minutes up to one meter depth.
The iPhone 7 has external dual stereo speakers. This change made a big difference in sound quality compared to that of the iPhone 6s. See why the iPhone is so expensive.
The iPhone 7 has no headphone jack. The lightening port now can be used for both charging and listening to music. This is why you can't listen to music while charging the iPhone 7. In order to use your old headphones, you will need to buy a converter.
The iPhone 7 is 25% brighter than the iPhone 6s.
iPhone 7 has stronger CPU. The specs are: Apple A10 Fusion chipset: Quad Core CPU, Six Core GPU, 2GB of RAM compared to that of the iPhone 6s which are: Apple A9 chipset: Dual-core CPU, GPU: Six Core GPU, 2GB of RAM. The iPhone 7 is thus faster than the iPhone 6s.
The iPhone 7 front camera specs are 7MP sensor, f/2.2 aperture, 1080p recording compared to 5MP front camera, f2.2 aperture, 720p video recording for the iPhone 6s.
The iPhone 7 rear camera specs are: 12 megapixel sensor, f/1.8 aperture, focus pixels, Optical Image Stabilisation, quad-LED (dual tone) flash, 4K video compared to 12 megapixel sensor, f2.2 aperture, Focus Pixels, Software Image Stabilisation, dual-LED flash, 4K video recording for iPhone 6s.
The iPhone 7 memory starts at 32GB compared to the 6s which starts at the 16GB memory limit.
The iPhone 7 design is almost identical to the design and the dimensions of iPhone 6s. The iPhone 7 comes with an additional color which is black. The iPhone 7 is stronger than iPhone 6s thanks to the new Series 7000 aluminium used. See also is iPhone 7 worth it.
The iPhone 7 has a slightly better battery. The iPhone 7 has a 1960mAh battery, which is slightly better than the 1715 mAh of the iPhone 6s.
The almost identical design has led to an almost identical weight. The iPhone 7 weighs 138 grams compared to 143 grams for the iPhone 6s.