Reaching for a cable costs a second more and would save around 10000 tons of coal per year (based on your calculation) if the equivalent of coal power plants were reduced by the same amount.
You can't have it both ways. If you're counting the energy consumption of 8.3 billion people consuming 15 Wh, 365 times, then you're also talking about "a second" for each, or 3 trillion seconds, or 95,000 years of time saved in exchange for that coal.