Taking a look at the specs is immediately apparent that the image sensor, a BSI-CMOS is now and, accordingly, should work a little better in low light, but I could find no real improvements. The biggest change inside is undoubtedly the new DIGIC 6, which essentially sets to work is than its predecessor DIGIG 5 in the G15.
One notices this especially during burst mode, which now provides a maximum of 12.1 FPS and in combination with UHS-I memory cards also constant at about 9 frames per second - no comparison to the G15! Unfortunately, this only applies to JPEG images in RAW mode remain little more than 2-3 frames / s over. In general can be JPEG, select RAW + JPEG or RAW only for storage. Once JPEG is enabled in any form is possible resolution and quality ("Super Fine" or "Fine") set apart.
Also, the video mode is with 1080p60 / 30 now been really nice in terms of frame rate, unfortunately, Canon has in the current firmware no Pal frame rates (1080p50 / 25) integrated. Otherwise, the video mode is only recommended: The image stabilizer does an excellent job and also allows out of the hand results which otherwise are hinbekommt only with a tripod. The built-in microphones have something to fight with wind noise, noise of the camera (image stabilization, AF) are, however, very well filtered. Accordingly, the sound but slightly overcast / is generally depressed. An external microphone can not be connected, unfortunately.
.......
Conclusion:
Who is in possession of a G15 should the G16 "upgrade" if he really expected a lot more in the area of speed or wants to connect his camera via Wi-Fi with your smartphone or tablet. The same criterion applies to "new customers" opt between the two cameras.
What astonished and delighted me: As a Canon DSLR users I have virtually no learning curve needed and could start right away. All the controls where I would expect it and grip!