In your scene you clamped all caustics and glossy+diffuse bounces are set to minimum.
Also highlights are clamped to 1.
In interiors I set glossy and diffuse to 10 or 12, for exteriors 5-8 and caustics can be clamped because the sun generates visible fireflies hard to delete with the pixel filter.
I never create materials with diffuse shaders except when I need translucency for thin surfaces. For plants I alway mix diffuse and glossy.
For example the curtain material is wrong. There is no transparency. In reality we should add an opacity mask or mix a diffuse shader + specular with roughness set to 0,1 and index set to 1.