Assuming you are using the "short" scale then 1.5 quadrillion is 1.5 x 10^15, which means that if you want to finish the job in a weekend of 48 hours, your computer will have to crunch almost 9 BILLION (9 x 10^9) iterations PER SECOND. Even with your superlative hardware I guess that is too much.
A program should be light and agile, its subroutines connected like a string of pearls. The spirit and intent of the program should be retained throughout. There should be neither too little or too much, neither needless loops nor useless variables, neither lack of structure nor overwhelming rigidity." - The Tao of Programming, 4.1 - Geoffrey James
My blog: Imperial Deltronics