Metabolism is directly related to body temperature in coldblooded animals (fish). They do not regulate their temperature the way we do. Because of this, as the temperature drops, they will become more sluggish, they will use less energy, and can ultimately die if not corrected.
You the answer to your question is no, they will have a lower metabolism, and thus would require less food, but only to a degree.
As a contrary example, when treating for Ich where the tank temp is much warmer than normal (87-89F), the metabolism of the fish will be increased. At higher temps they may appear sluggish (how would you feel on a 100F day), but their metabolism and caloric requirements are actually increased compared to typical tropical temps (78-82F).
That is the tradeoff with warm-blooded vs. cold-blooded. We can regulate our temp and survive for a while at relatively extreme levels, but they can survive for a LONG period of time at moderate extremes and require very little food compared to us.