14.9's possible in an Si, but there's steps you have to go through.
First off, you have to use the right stuff. Okay, an Injen Cold Air get's more hp to the wheels then an AEM, if everything's stock. But tests have proven that when you have a ceramic coated JDM header AND a cold air intake, the AEM one responds better to the set up than the injen. So an AEM gets about 5 hp to the wheels, stock, and Injen gets 6, but with the header, the AEM get's nearly 7 wheel hp, and the header gets more hp as well. It's all in set ups, so say you have an AEM cold air, a DC sports JDM type header and Greddy catback exhaust with a high flow cat, with minor weight reduction it's possible to break 14's, especially if the driver is good. With a shortshifter it's even more possible, because I've driven Si's, and you kidrocket have to know the stock Si shifter isn't too responsive to powershifting, but with a shortshifter, (a real one not an autozone one) like the B&M, you'll take 70% off of your shifting time, and if it normally takes you 1/4 of a second to shift gears, and you take 50% of your shifting time off, then you just knocked off 3/8 of a second off your 1/4 mile time, because there are 3 upshifts in a 1/4 mile run with an Si.
An Si stock off the lot runs 15.7, broken in and taken care off with about 3000 miles on it, it can run 15.5 with good track weather. (everyone knows a car runs better when it's broken in and it is taken care of)
And intake header exhaust is known to drop .3-.6 of a second off your quarter mile time.
Hope that helps.