Flocculation is a method to standardize your results, but the multiplier is variable depending on the cheese. So yes, if you are using a multiplier of 3 then 15 x 3 = 45 minutes to curd cut. That is total from the time you add rennet.
You can adjust that multiplier for different types of cheese or to suit your preferences. In general, a smaller multiplier will end up with a drier cheese. A larger multiplier will end up with a moister cheese. This happens because curds that have set longer will retain more moisture. So, you could use a 3.5 multiplier and get a moister Gouda.