I think the fireflies are mostly due to your lights being ONLY at 60, this is a very small number for filmic, it produces a small amout of light rays hence you get the fireflies.
What I did was crank up the lights to about 3000 to get plenty of light in there, that got rid of majority of the fireflies, I also added a weak sun lamp to add some extra ambient light.
Than I went to the compositor and used curves to bring the render closer to the draker moody lighting (I assumed that's what you ware going for)
Either way the settings can be tweaked in the compositor as you please, the scene is not over exposed by any means so you can take the curves node off if you prefer it brighter. I'll attach the modified blend file:
Keep in mind that firefly free does not mean noise free, if you don't want to use the denoiser be perpared to render each frame at like 4000 samples or higher (even than I don't know if you'll get rid of all the noise)
Here is a render at 512 samples:
As you can see there is no firelflies but still plenty of noise.
Using the denoiser for animation is not as bad as people make it out to be, it mostly gets lost in compression. I've rendered out a section of your animation at 128 samples and half the resoulution with the denoiser on: https://youtu.be/Rs4SdF9vNUU
There was some flicker but it mostly looked like film grain and in this youtube clip most of it got lost in compression anyway. If you up the samples to 256 or 512 it will definitly look fine, maybe not perfect but it's better than rendering for a month.
In the end it's your animation so you can do whatever you want with it, either way the fireflies are fixed.