An average man is locked in a room with an adult hippo. They respawn fresh if they die. How many lives does it take to kill the hippo?

The room is 15x15 feet, well lit, and completely empty. The hippo is a regular healthy hippopotamus and it is not blood lusted or anything like that. The hippo keeps all accumulated damage. The man is naked and doesn't have any kind of weapons at all, but upon death he will respawn in 5 seconds completely refreshed away from the hippo. How many lives / how long does it take for them to kill the hippo?

R1: The man's corpses persist after death. R2: The man's corpses disappear once he respawns.