this was particles from an emitter object, I'm trying out hair now (does the same thing), instances don't seem much faster from what I tried right now, they also clutter up my scene. With a large lawn with more layers of plants, I could end up with millions of objects in my scene and I also lose a lot of procedural control when freezing the hair sim.
If it isn't possible to speed up the export process for hair and particle emitters, would it be possible to somehow keep the data that hasn't changed between renders, so it only has to be exported once?
With multiple layers of greenery as separate particle systems, this would make sense for doing test renders.