It is because of TouchWiz, I also tried it on SGN3 and saw RAM occupied 1.8 GB of RAM So I recommend putting a ROM, if you stick CuyanogenMOD will consume much less RAM, and on top is CyanogenMod 11 You go To Fast To Furious, ATTENTION AH if you put the warranty CyangenMod perederá and nobody will take responsibility if the mobile is damaged putting a ROM