I managed to make Freestyle rendering much faster by playing with some settings, finally I can render images in reasonable time. Freestyle is really weird, the main image renders in
two minutes nano seconds after I spent far too much money on a new GPU last year and then it takes 15-30 minutes to draw some lines over it. That behaviour is really weird but easily explained by the fact that Freestyle can not utilize GPU at all and only one CPU core which I sincerely hope will be remedied in future Blender 2.8 releases. It seems like something that should be possible to run on parallel threads and frankly I always thought it would take far less effort than it actually does. Still, the technology itself is amazing and I love the results it produces, even the comparatively long render times are nowhere near what I would need to draw even just the lines by hand, let alone the actual images.
As always here’s a list of models I used, a big thanks to anyone on this list for being awesome and sharing your models!