HELP...G Flex2 Diesnt have smart screen mode!!!

Hi eveyone.I have just bought a lg g flex2 at&t unlock version.But,I realized that there isnt a smart screen mode at the screen timeout menu.(It closes every fifteen secs. And dont want to close the screen when its lookin)
The fw is 5.0 lollipop.This version of g flex2 (at&t) doesnt have this feature??
Or android 5.0 has a problem??
Help please...