I've got this so far, but the victim is not teleported back to spawn. It just cancels the death event and can keep on "dying".
Code:
on death:
attacker is a player
if victim is a player:
cancel event
add 15 to the attacker's account
teleport victim to location at (25, 98, 5) in world "Main"
broadcast "&c&lPVP &7» &c%attacker% &7killed &c%victim% &7and got &a&l+15$"