Framerate drops when I preview my game, what is particleSystem.renderSingle in profiler?

Hey, I'm creating a tour of the blood vessels in Unity, I used a mesh particle emitter to emit the red blood cells and other elements which flow towards the camera. However every time I play or preview it the framrate drops to about 6fps and the profiler shows that that camera.render is at 98%. Any idea on what I could do to fix this and get rid of that lag?

PS. I'm new to Unity, any links to basic optimization tutorials would really help, I would search them myself, but I wouldn't exactly know what to look for. Thanks!