6 lbs in 2 weeks is doable. Rule of thumb is 2-3 lbs a week.
It also depends on where your starting from. Someone that's 30% Body fat could lose that fairly quickly...however someone that's 10% bodyfat could take a little longer and might lose some muscle if they try to quickly.
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Depending on how much you weigh,3lbs a week is ok...people who weigh more tend to loose faster and more lbs per week then someone that has only a little to loose
Just make sure that you are getting enough calories from good foods to sustain a good healthy loss