Based upon your other post, you have about 200 sq-ft of panels. I usually use a rule of thumb of about 1 GPM per 10 sq-ft of panels so in your case that would be 20 GPM total. That is the upper end of the range they gave you.

You said that you have a 1 HP Hayward pump. Is that a 1 HP Superpump?

Also, what is the actual pressure reading with and without solar?

How high are the panels installed?

Do you have separate suction lines coming to the pump?

What size is the pipe for the solar panels?

2 PSI rise could be reasonable for your setup but it depends on the answers to the above questions. However, forcing all of the water through the panels may not be necessary given you only need 20 GPM.