It really depends on where you get shot in the body, If you get hit in the lower stomach then it would take a decent amount of time to kill you but if you got hit in the heart it would take less than 15 seconds, Personally I think it should be made if you are re balancing them is to correlate the damage to the caliber of the weapon, The Barret would deal the most and would one shot to anything besdies arm shots and could one shot an RPG to the chest. I think making the orsis somewhere in the middle would also be a decently smart idea, It should go that orsis/ mosin are able to 1 shot to the head and body and not one shot to arms/ legs, Base faction snipers should be able to one shot to the head and not the body and the SOC factions should be able to 1 shot head and body besides tier 1 factions, which would one shot to head body and legs.