This question has been asked a few times before, but even after following tutorials such as this one
and following the settings, I've been unable to get rid of fireflies in my render. The current render looks like this: 
What additional steps can I take to decrease the amount of fireflies / reduce graininess in my renders? I've tried clamping and all of the other techniques in the tutorial but it doesn't seem to help, or at best, has a minimal effect.
Here's the model itself. It's pretty simple, no textures (just shaders).

For reference, the blend file is here: https://transfer.sh/yITqe/spaceship.blend
