I´m a brazilian player and one of the annoying things when I´m playing online into a room with US players. Whenever you need to spend a lot of ammo to kill an enemy. They kill me with a few shots as I need to use almost an entire cartridge.
There are a couple of things you can do to help that. First check your router settings and make sure they are at optimum settings. Second use a good loadout like rapid fire and a grip. This will improve fire rate and accuracy. Thirdly and this is most important, slow down. Most players dont do well because they move through the map to fast and dont realize their being seen. Good luck and hang in there.