I'm not sure I'm following. Is that a MDX Query? It doesn't quite seem to be following MDX.  I don't see where you're specifying rows and columns.  The functions don't seem to have the correct syntax as well. 

In my rows I want to have TOP 15 Payer names  sorted descending by Payment Amount.  In my Columns I want to have Payment Amount, and Percent of Total (which shows what percent each of the top 15 payers have paid of the total amount) The total amount is not only from the top 15 payers, it would be from many more than the top 15.