4.6 -> 5.0 Dramatic Performance Loss - No batching?

After upgrading my project to 5.0, this scene runs dramatically slower. I'm talking down from 120+ frames per second down to 30.

The scene is comprised of many transparent sprite renderers, billboarded towards the camera (although disabling the billboard script has no significant effect on performance. It seems like the problem lies in batching. Previously I would have seen ~1800 calls saved by batching, now the stats window says 1 call saved. Changing shaders doesn't affect it, nor does using the deferred renderer.

Turning off shadows improves FPS quite a bit, but still the scene isn't saving any calls with batching. Any ideas?

Edit: Added this screenshot to compare versions, although the 5.0 FPS is 74.2 here, it does dip to 30 in other areas.