With selective breeding you could technically be lucky and slow down the metabolism, selective breeding isn’t a very precise way to change something, but the actual problem would be time anyway.
The problem is that any change slowing down the metabolism would be deleterious in nature: no/slower body heating, lower brain capabilities, slower healing, increased reaction times, etc.
As a rough comparison, it’s like trying to reduce the energy demand of a computer. There’s some room for optimisation but eventually the only way to do it is by reducing the amount of things that it does, by throttling its components.
Moore’s Law has no good biological equivalent. And it doesn’t even refer to energy consumption itself, but the number of transistors in a circuit.
