My band had a problem where our PA, using ZLX-15P and ZLX-12P, would trip GFI's at various venues. GFI's trip generally when leakage current from the Line/Return path to the PE ground (that third prong in the US) exceeds 4mA to 6mA, depending on the GFI outlet (they vary, apparently).
After purchasing a clamp current meter capable of reading leakage, along with a HT Line Splitter to measure the leakage to the PE, I found that all 4 of our ZLX-12P and ZLX-15P speakers each had around 0.45mA of leakage. Our subs (EKX-18P) only have about 0.15mA of leakage. All together, our PA is sitting at 3.0mA of leakage from Line to the PE. That is with no music! Other equipment added some and, lo and behold, we were just at or a little under that 4mA. Right on the verge of popping a GFI.
I contacted EV Tech Support to see what the expected leakage was. I did not get an answer on that. What I did get was a statement saying the ZLX and EKX speakers will likely trip a GFI and they should not be plugged into a GFI outlet. Nothing more than that. They terminated the chat, so, I didn't have a chance to get more info.

Two ZLX-15P speakers, if they only leak 0.45mA, may not pop a GFI, unless the GFI is too sensitive. Two, plus four ZLX-12P, and a couple of subs, will likely pop a GFI when blasting sound. I have not made measurements of the leakage at full volume yet. It is probably pointless, as EV states that these speakers have problems with GFI's. The answer is to find an outlet with no GFI, or use a ground lift (your call on that one).