Take a look at this table Click Here and you will see that your onboard card shares its memory with the 2Gb you have installed. The 6200 is a dedicated card with its own buit in memory and so will not place such a burden on your system memory. On the other hand the clock speed and other stats for the 6100 are better than the 6200. Personally I would not use the 6200 but I would increase your 2Gb to at least 3Gb.
Samsung Galaxy A8 review: Hands-on