I use my f/2.8 IS in mode 2 all the time at races since it helps stabilize the vertical shake while panning.
Can I achieve the same results without IS? Yes, but the hit rate may not be as high. But you'll have a mind-numbing number of laps to capture the same cars, so the hit rate may not be as important.
IS also comes in handy when shooting static scenes in the garage/paddock areas that may be poorly lit.
It really comes down to how you value your money, but I presume $15 is a bare fraction of your total outlay for your trip to Indy (it probably won't even get you a decent meal at the track).