How much should I reduce the liquid in my recipe if using quick-cooking barley?

I am making a barley and mushroom "risotto". it is in the vegetarian version of the joy of cooking cookbook. one adds one cup of pearl barley adding 2/3 cup of dry white wine and then 6 cups of vegetable stock, a little at a time because the recipe says that barley takes 45 minutes to an hour to cook. But I am using Quaker quick-cooking barley and the box says it cooks in about 15 minutes. So how much should I reduce the amount of vegetable stock (and wine if necessary) so my risotto comes out the right consistency? please answer asap if you know how to help me! I have to start dinner in about an hour and a half! answers plus tips if you have them would be greatly appreciated!