Currently our system has 2 zones running off a lake pump with each zone having about 13 2.5gpm rotors and 3 1gpm sprayers (about 35gpm added up but have no idea what the actual outflow is yet). I want to add a zone for a garden and shrubs but this will only have a total rated flow of around 10 to 15gpm. I'm assuming that the lower flow will increase the pressure and I'm wondering if this will cause the pump to overwork by trying to push against the resistance. There isn't a pressure tank involved here.

Or am I closer to the 10 to 15gpm mark on the original two zones no matter what the heads add up to due to the pipe diameter? The system runs 1-1/4 inch pipes from the pump but everything I've dug up so far is either 3/4 or 1/2 inch pipe.