Why would I being getting low fps in a build but not in the editor?

I'm having a bit of a performance problem. While testing and editing my game in the editor, everything is smooth, but as soon as I build the game, the FPS goes down the drain, to around 20. My questions would be

1) Has anyone else come across this? 2) Could it be a new bug of some sort? 3) Are there any fixes that you know of?

I've messed around with the quality settings, camera effects, and other stuff, but there hasn't been a change. I'm tearing my hair out over what this could be.

It's a relatively simple scene with few shadows and some pathfinding, so complexity isn't really a problem.

Computer specs, so you don't have to ask- Quad core i7 GTX 860m 16gb ram (it's a laptop)

Ask and I'll include more specs, the screenshots of the scene if you need them