The GX1 / G15 question ?

I would love to simplify my kit to a single camera with no lenses to lug about.

The GX1 and G15 are high on my desirable list however they have created in my mind a dilemma as one has a large sensor and the other a faster lens hence my question below.

For exactly the same lighting conditions which set up produces the least noise.

GX1 at F2.8, ISO800 with the 14MP 1.5" CMOS sensor

G15 at F2, ISO400 with the 12MP 1/1.7" CMOS sensor

Any views

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bjc