just wanna ask, is it necessary to install antivirus into s3??

hi guys, wanna ask.. my s3 is not smooth (lagging) when swipe from one screen to another.. why ar?? just bougth it last week.. didn't root or do any configurations on it.. still belum pecah dara lagi.. can say everything is stock condition, except got arund 2-3 games & 7-8 basic tools & apps like clean master, adobe flashplayer, adobe reader, whatsapp, fb, quickoffice, navitotal, instagram, quickoffice, that's all.. i did compared with my frenz's s3 & note1, both still in stock condition but got lost of stuff on it, but can feel their phone is very smooth when swipe from one screen to another..

one more thing, i checked in my s3 task manager, for RAM usage, it shows max is 779mb only.. is it standard for stock/ standard s3??

sorry, noob questions here.. still playing around with my s3..

hi guys,
found out Power Saving Mode features caused of it..
disable it, then mo more lag...
thanx guys for giving hands.. thanx a lot!!..