Are the Toro 15 foot heads full circle sprays (360 degrees) ?
If they are...they EACH use more than 2 gpm...hence your problem.
The full uses 3.6 gpm....you are trying to use 3 times the amount of water available...even if you had 200psi this won't work.
The half uses 1.65 gpm.....you can't even run 4 1/2 circle nozzles to get this to work.
I'm not sure what you did wrong with the design guide...but it is time for "do-overs".....
Sprinkler Solutions, Inc.
Arizona and Colorado
www.sprinklersolutions.net