Me and the other photographers that do this work travel with specific equipment where we have a pretty fast paced schedule. I use a flash, full power just to soften the shadows and at f/16 you would need multiple high power strobes to over power the outside light plus that would over power the interior lights which need to appear on as well. Big flashs or strobes inside creates obvious strong directional shadows where you can usually see that in your images and thats not what the company I work for wants. I Don't always use/need the polarizer filter inside but it can really improve the pictures as the furniture and artwork just turn white from the reflections of the outside light. There are other ways to approach these types of things but I'm set on a pretty demanding schedule where there's just not enough time to spend hours in one area. So far I've done thousands of images like this but sometimes it just means more work in Photoshop which I'm trying to always shorten that time down.