You could try adding and scaling a floor zone to the interior and setting forcesimpleobstacle = -1.
The tiling is likely something to do with the model and the UVs rather than needing mipmaps.
If the level is entirely set indoors, you could also change your sky box and terrain to match the colours of your indoors to stop getting grass reflections on the shiny revolver (reflections are from the cube map auto generated from selected skybox and terrain).
Cheers.
GPU: GeForce RTX 2070 SUPER PassMark: 18125