There are two optimization methods that can do a lot to decrease render times in Maxwell Render. One is to not use large surfaces such as walls/ceilings/floors with too high Diffuse values. The other optimization is to try and keep all Emitter surfaces as low poly as possible. In most cases a single sided poly plane will be sufficient.

The following images illustrate the amount of noise decrease just by taking care of these two optimizations.

The left image shows the walls/ceiling/floor with a Diffuse material at RGB 240, and spherical emitters for all lights. Compared to the image on the far right, there is substantially more noise.

RGB 218 was chosen for the middle and right images because 218 approximately represents the reflectance of white matte paper. You could of course put this up a bit further with only a small increase of noise, but using 240 or more for walls and ceilings will not produce realistic results and will increase noise levels.