/3/ - 3DCG

>>648232
Turn on particle collision. Assuming they're just textured planes, you should be fine without chugging too hard.
Does it really matter though? Depending on where they are in a scene you probably won't notice it. Hell, it's hard enough to really notice here unless you really look for it. The more glaring issue is how homogeneous the leaves look.

Make a few more variations, some curled up, some broken up, and some different colors.
You can get some different colors pretty easy by setting up a color ramp that defines the colors you want, and hooking a "random" node up to it. So every instance of the object will have its own color that falls within the color ramp. Throw some slight SSS up to your leaves and they'll look pretty good.