Turning particles off slows down rendering?

I have an environment with opaque geometry and a generous amount of particles.

There is a script that toggles the particle systems on and off. Turning all particles off improves FPS - but only by a few percent (on an iPad Air).

Looking at the draw calls in Xcode I see that the transparent particle calls have indeed disappeared, but now all opaque draw calls take twice as long (right side of the screen capture below)!

Is Xcode reporting wrong values?
Is Unity deciding to spend some extra quality time with the opaque geo?