Because our economy is extremely oil-dependent, we'll be able to take the upper hand in this conflict?

That's not exactly what I said, and a long way from what I meant.  On the other hand, the low efficiency of use of petroleum in cars and light trucks (less so in large trucks) leaves a lot of low-hanging fruit.

Remind me again how we're going to get oil down to $15 a barrel?

We may not be able to, because other consumers would keep it bid above that price even if our consumption fell to zero.  But a serious decline in oil demand caused by greater efficiency and substitution of other energy sources would limit the price it could command while simultaneously limiting the amount that it was economical to pump.  The damage to the income of the oil dictatorships would be devastating.