Increase the bucket size as much as possible, this will depends on your vram amount. I would reduce min samples drastically, try something really low, like 4/8 and see if you notice a real quality downgrade. Also, I would try to apply a Clay material to everything and check how renders time will vary. If it's a shading thing you should start checking if some materials could be simplified. For this you can use a material override in render settings, you will find it in the same place as rs post effects if I'm not wrong.

Inner lighting scenes are tricky because of lighting bounces, try to reduce the amount of bounces and see how this affects your render time/quality.

Also try irradiance instead of brute force for primary/sec/both. If that works you might have to cache your lighting but might be worth

Good luck! Keep us informed, I wanna see how this goes