Best Way to do Cookie Persistence here?

The content on all the "pools" is the same. I misspoke above about the first request.

 

 

As I mentioned, we have 5 pools, each with 3 servers. We also have a pool that contains all 15 servers. The iRule should check to see whether the cookie exists, and if it doesn't, send the request via least connections to the pool containing all 15 servers. Then, the iRule should check the IP of the chosen server, determine which pool it's in based on a datagroup or something else, and set the corresponding cookie.