Fetch XML query with older than 15 days / 2 weeks

Hi,

We are trying to find a way to create a custom view showing all records that have not been modified within the 2 last weeks =  which could be modified on - greater than 2 weeks.

But in Fetch XMLSchema in http://technet.microsoft.com/en-us/library/gg309405.aspx , they only propose an operator with month.

Does anyone has a solution..

Thanks

Ivan