This is a question of math.
What is the source?
What is the size of the mainline?
How many gallons per minute do the sprinklers flow?
What is the pressure?
If you do not know all of these answers, you can try combining 2 zones and see what happens to the performance.
I mean taking 2 zone wires at the controller (take zone 2 wire and add it to zone 1)
See what happens, you should be able to get an idea of the performance, also check this at different times of the day to see if the pressure is different.
Keep in mind this may cause additional wear on the timer, depending on the quality of your timer.
Good Luck.
If the changes look terrible, you can always reverse it.