Yes, interior renders in Maxwell do take a long time to clear up generally. But as well as using window emitters, keeping the bulb emitters really low resolution, I find the denoiser to be great.
Depending on the model of course, I'm getting usable renders in around 2 to 3 hours at a resolution of around 4096 x 3072 or there abouts.
I usually set the denoiser to Fast at each SL starting at SL6 so I can get some feedback. Some texture maps such as woodgrains etc. can suffer, but clear up after some extra time.
I have been in a discussion with Mihai Iliuta who is ex. Next Limit and the best resource I know on Maxwell Render, he also has his own training resources that I promote http://bit.ly/2EzJP5kaswell as those on his site http://www.maxwellzone.com/
The issue is that Andrew West has published some comparative renders done in the new Vray vs. Maxwell render with much different render times that make Maxwell seem slow.
The discussion went basically that he was not using the Denoiser, which could remove noise quicker for faster test renders but had issues with the results being 'smudged', which seems to be a current issue in v126.96.36.199 Andrew asked about the Maxwell Material library? The smudging of your woodgrain could have been fixed with simply "redenoising".
I must also add we are all waiting for a new version update to fix this and some other GPU related issues that will make much faster render times possible.
See the following;
About Andrews post, you can reply to him that there are really two bugs with the denoiser right now. One is an outright bug, the other is more a bad implementation because they don't (yet) give us control over how heavy we want the denoising to be.
The bug is easy to get around. You can tell him to simply press the "Re-denoise" button in Maxwell Render, after the render is finished and has already denoised the render once. Let the denoiser run again, and he should get a much less smeared render.
About render times, I can say that his final Vray render will not take 14 minutes, or close to that. In his scene, what he should do first of all (for both Maxwell and Vray) is to create more realistic materials that have reflections. Almost every real world material has a bit of reflectivity, especially the wooden table, the dark painted (what looks like) metal beams, the floor, the ceiling, the window sills...everything. Once he has finalized the materials, he should run another test in Vray with settings that don't make the reflections look noisy, or blur the definition of shadows too much. Of course it will be faster than Maxwell but not by such a huge margin. He could get a very similar test render with Vray for this scene in 3 minutes if he wanted...
Once Maxwell has MultiGPU, additive materials work on GPU and the denoiser issues are fixed, I think people will take another look at Maxwell. There is no other renderer that is as good out of the box at archviz, jewelry and product design, and even VFX. An interior archviz render like this example should only need about SL (Sampling Level) 13 (which is actually rendered twice, the denoiser works by comparing noise in two different images), and then the denoiser does the rest. A typical interior render needs about SL 18 to have acceptable noise (which would still need a bit of denoising in Photoshop), SL 14 is reached approx. 16X faster because each SL level takes twice as long to reach as the previous one (SL 13 rendered twice is equal to rendering something to SL 14, time wise).
So a good working denoiser means already about 16X faster render + you can buy a box of 4 GPUs for about the same price as a high end computer, and in my tests so far the GPU renders even a complex interior about 3X faster than on my CPU, thus 4 extra GPUs would get me 12X faster renders + 16X faster from the denoiser - around 28X faster rendering, for a relatively small investment.
Regarding the Maxwell material library, there are fewer materials there now because it has been curated by NL staff so that only good materials are left and also those that have proper textures.
Andrew responded that he found the Materials editing time consuming and had not found a way to currently get Maxwell to render faster ( see forum : http://forums.formz....revisited-vray/ )
Mihai responded with this reply;
Andrews reply in that thread is something typical I've seen over the years: I need something in 15 minutes that I can show to my client because they make a lot of changes. And for some reason they have no problem doing a preliminary test in Vray and show them a render that's far from final quality, but every test with Maxwell needs to be rendered completely noise free...people freak out about the slightest noise in their render, even a test, and even more than they would in a digital photo that has plenty of noise if you look closely.
So this is yet another area where the denoiser in V4 can be really useful. They can let the render run to only SL 9, run the denoiser and show the test to the client. It will be a little blurrier than the final render (SL 14 + denoiser), but as a test it's perfectly fine and it will be noise free because of the denoiser.
In summary you can reduce render times in Maxwell but care in the set up and not pushing the limits for test renders and with a little wait for a new version that will make GPU rendering more viable and super fast.
Mihai is a great resource, very knowledgeable and it is worthwhile mentioning the Maxwell Public forum - https://forum.maxwellrender.com You need to login but it can be great resource.