Here is a bit more to this weight issue....
The criterion for minimum weight is actually 6.8 kilos which is closer to 15.1 lb. This was established in 2000 with the objective of making sure that no one racing would make their bikes so light that they would be structurally unsound, fragile and dangerous. What they did not foresee at that time was the significant advancements of carbon fibers which mean that the weight could in fact be reduced while still being quite sound. Thus back to my earlier comment.... if a structurally sound bike can be built that only weights 5 lb (and they are in fact at that point now), this simply means that the potential size of a battery (that when inserted still allows the bike to remain below the minimum weight criterion of 15 lb) could weigh as much as twice the weight of the bike itself.... 5 lb bike with a 10 lb battery in the frame. Crazy, huh?
Yes, crazy!