a lot of people keep asking me this, and it was mainy i think cause the turbos were cheap and it sounds cool, but have a read of this, it makes a lot of sense and actually gives reson for twin turbo being better for a ROAD car than a single turbo

from www.autospeed.com

Twin Turbos
For mega-horsepower turbocharged road cars, it is normal to pull off the factory turbo unit and replace it with a monster turbo. While this gives smooth boost response and excellent top-end torque, the trade-off is a loss of low-range (and possibly even mid-range) torque and an accompanying loss of transient response. So yeah, a single big turbo will be great for cutting loose at over about 120 km/h, but at normal urban speeds it's likely it won't have the low-down boost to produce much torque. You might find it a bit embarrassing to own a genuine 500hp car if you can't keep up with 300hp cars in everyday traffic...

Take a look at any factory-produced high-horsepower turbocar and you'll see there's always more than one turbo under the lid. This isn't by chance - they're made this way to achieve much better low-down torque and turbo response, while still retaining similar top end to a massive single turbo installation. So if you ever decide you want to get lotsa power from a new turbo system, ask yourself if there's enough room to fit two (or more) turbos.

so how do you like them apples

it's true what it says, i remember my bro's starion (a little old skool but still) it would make positive boost at 80km/h in second gear, this meant he never really used boost, cause when it arrived he was already on the speed limit, basically in the every day driving around suburban roads it was pointless, the only time he could really use it was down the occasional freeway on ramp

the tt-a12 on the other hand i found was completely diffrent, and i hope the a15 is too

anyway thats some interesting reading for ya