I've said it already today on here but these pictures are making me excited about getting my S6 tomorrow, I can't wait to have a decent camera!
You'll love it!

Two ways to do it. Either install AIDA64 and go to the Devices tab and see what Camera ID says at the top. Or do this:
How to check your s6 camera sensor:
Dial *#34971539#
Look for ISP VER CHECK and click it.
Sony IMX sensor will be SONY_IMX240_FIMC_IS
Samsung ISO sensor is SLSI_S5K2P2_FIMC_IS
Mine has the ISO sensor. Better low light images.