Is room size considered when they design speakers?

Never see speakers saying best used in a 15 x 15 room.   
Also, why do speaker cabinets tend to be larger as they get more expensive? Not easy to answer. I know bigger handles bigger drivers but is this the only reason?
So no. Your response is no. Keep “crafting” pal.

"What is that like, third grade? No. Actually a lot of third-graders write better."

Hanging around school playgrounds a little too much?

To craft your clever prose a little more readable, how about this...

"What is that like? Third grade? No. Actually, a lot of third-graders write better."

Looks better? I know, you may need to stay practicing during recess.
This is just my guess. I think that to a certain extent they consider the room size a certain design is optimal for. I don't think they would expect a customer to use standmounters in a large room, for example. Same as you cannot use a Tannoy Westminster in a tiny room. They don't go as far as providing room measurement specifics since it may cause audio nervosa and potentially turn away some customers because their room does not measure 15 x 15. 
I am not sure how they go about sizes, but they do not seem to care as much about speaker placement and room treatments as Audiogon crowd does...

Loudspeakers by DALI - Award-winning Hi-Fi speakers (

Wilson Audio - SabrinaX
I am of mind to say larger speaker size should get along with smaller and larger living type rooms.  SQ in a smaller room can readily handle a larger high end speaker.  
I don’t want to know sound is coming from speakers.  Larger speakers do better filling room. Secret is to get speakers away from walls, and smaller rooms limit this.  Just want sound to fill room, hate dealing with sweet spot issues.