I do not know the date of this question, but if it is correct then the Wikipedia entries must since have been amended.

Look up the Wikipedia article "Long and short scales". It covers the subject very informatively, in fact very impressively. 

In response to the direct question, if you are working in the Long scale, then a thousand billion is indeed 10^15, whereas in the short scale it is 10^12.

Two comments here: Firstly the famous collapse of George Dubya upon being advised that a Brazilian had perished in Iraq. Upon his resuscitation he managed to gasp, "how many's a brazillion"?

Secondly, as the National Geographic and Discovery Channels constantly iterate, to the extent of my being driven to distraction, is that tens of thousands of smaller units of measure sounds more impressive than fewer larger units. For instance you will never, ever hear of (say) a Boeing 747 weighing a mere 480 tonnes; it will invariably weigh 480 thousand kilograms, with a special, contrived nasal exaggeration being placed on the "thousand", or the height of stupidity even 480 million grams !

If you are conveying plain facts these days it is almost universal that thousands, millions, billions, trillions etc. are multiples of a thousand. On the other hand if you wish to try to impress your audience by making numbers sound high, do what TV does and confuse and irritate everybody.