Does slowing down a simulation do harm? If/​when time for computation becomes exhausted, those beings who lost the opportunity to be simulated are harmed, relative to the counterfactual world in which the simulation was not slowed.
Slowing down a simulation also does harm if there are interactions which the simulation would prefer to maintain which are made more difficult or impossible.
Slowing down a simulation also does harm if there are interactions which the simulation would prefer to maintain which are made more difficult or impossible.
The same would apply to halting a simulation.