Your question is a little ambiguous. But, to clear up one of the ambiguities, I think we can assume you mean if the bunny had been powered by a single C cell, continuously, 24/7 since the first commercial. Since the bunny was robotically controlled, and they even state that it's a simulation, I think its fairly safe to say that in actuality, it was using a lot more power than what was provided by the single battery. But, I'll still focus on the solution for just one battery.
Depends on how quickly the power was drawn from the battery. I.e., a battery will last for months in a smoke detector (very low draw), but the same battery might only last half an hour in a high powered toy. We'll assume that the toy draws a high current from the battery, causing the battery to last no more than 30 minutes. So, 2 batteries per hour, or roughly 50 batteries per day. An alkaline C battery contains about 10 watt hours of energy, so each day, 500 watt hours of energy. Or, every 2 days, a kilowatt-hour. So, in a year, about 180 kilowatt hours (since I rounded slightly up to 50 batteries, I rounded down to 360 days in a year) And, in 15 years, that would be 2700 kilowatt hours of energy. Or, about $270 in electricity costs if plugged into a 100% efficient transformer.
And, thanks. This will make for a really nice open-ended physics question that makes students do a bit more thinking than a typical plug and chug type of problem. Also, from the first assumption - a battery would last 30 minutes, you can easily change the final answer based on any correction to this. If the battery lasts an hour, then half the total energy. If the battery lasts 20 minutes, then 1 1/2 times as much energy, etc.
