There are two ways:

1. Create a view where you filter for the value of the last modified field, and compare it to the value of [today-15].
2. Create a view with calculated column with filter =[Modified]+15, and its return type is DateTime, which will returns the documents changed within the last 15 days

more information on creating view and filter is here http://blog.pentalogic.net/2008/10/advanced-sharepoint-view-and-filters/

There are two ways:

1. Create a view where you filter for the value of the last modified field, and compare it to the value of [today-7].
2. Create a view with calculated column with filter =[Modified]+7, and its return type is DateTime, which will returns the documents changed within the last 7 days

more information on creating view and filter is here http://blog.pentalogic.net/2008/10/advanced-sharepoint-view-and-filters/