Where's your evidence for this?
In the animal kingdom, isn't death due to predators rather quick?
In factory farms, the animal's entire lifetime is one of outrageous torture, e.g. feeding cows a corn diet that shreds their stomach wall, and forcing them to stay alive through the pain with massive courses of antibotics. Or keeping chickens in cages so small they can't even turn around.
Few predators "finish off" their prey though they may often kill it during the hunt, once the prey animal is disabled they start to feed.
House cats, for instance, will capture, release and recapture the prey animal, sometimes for hours.
Wolves and Dogs will hunt and not feed, often leaving the prey animal to die from it's wounds.
Also look into how predators teach their young to hunt. It is very unpleasant.
I'm not saying that factory farming should be allowed. In fact, I think future generations will correctly judge us harshly for the unnecessary atrocity that is modern agriculture.
Not always. A lot of predator species are known to play with their prey.