I have used Canon G5 before (quite similar to your G6), & your photo could be improved by the following pointers:
1. the iso of G6 has a minimum of 50, but your iso is not displayed but looking at the noise in the sky, I suspect the value was 100 or 200,
the sensor size of the camera is small i.e. 1/1.8" for 7 mega pixels, so I would recommend sticking to iso 50 for night shots;
2. your f stop is 3.0, a little suggestion of using a smaller aperture like f5.6 or f8 to render sharper image, better depth of field focus & especially purple fringing which is inherent with Canon G5 & G6 when one uses large aperture like f2 or f3 for night shots....this you can see from the bright white lights of the building signs with blue edging.....f5.6 or f8 will minimise this effect;
3. your camera is capable of low shutter speed of 15 seconds, you used 2 seconds, so there is a window of opportunity of up to 3 or 4 stops you can benefit with either lower iso (50) & smaller aperture of f5.6 by using the 15 seconds speed. A word of caution, use a tripod & the camera's 2 seconds shutter release delay to prevent hand shake after engaging the shutter button.
Hope the above friendly observations are useful......best regards from Kuala Lumpur