There are a couple of options. The first is to use a relative date filter and set it to the Last 15 Days:
Another option is to create a calculated field similar to the following:
if [Order Date]<=today() and [Order Date]>=dateadd('day', -15, today()) then 'true' else 'false' end
Then, place this on the filter shelf and keep the 'true' items only.
Hope this helps!
Thank you so much, Tracy!