Not sure this room requires a 12 x 15 rug As long as the front feet of the seating are on the rug you're OK.

No matter the rug you select IMO the dark brown/black wall dictates that there should be some black accents in the rug so your selection doesn't look so very random.

Here are room similar to your layout.

What a pretty space! Before determining the rug size needed, perhaps revisit the furniture layout. Consider shifting the two chairs to be in front of the fireplace to soften the look at that end with all the dark going on. Then place the sofas in an L shape at room center (one on left wall with the other turned to face TV) with a round coffee table to accommodate them. Revisit sofa pillow colors after rug selection is made to add texture and pop of color.

REally that dark wall does not IMO work at all in that space it is depressing . Waht possible use are the wall units except obviously to put stuff in with no real purpose. 2 low cabinets one on either side of the FP with the TV mounted above one and a nice piece of art above the other would IMO look 100x better . As for the rug why do you think wool is better than what you have as far as material is concerned . I think almost any rug can work in that space I might evne look at a shag for some texture . You need a pad under any rug you get I like felt pads they work well add a bit of comfort and with wood floors a must . The layout as it is is not inviting looking or good for TV watching any of the layouts Beverly suggested would be better .. You need lighting for sure art on the walls end tables and a coffee table that can be reached from the sofas so thta means pieces pulled into the space ir a really huge coffee table

I know you're just asking about a rug, but desigers and others who comment take the whole room into account, not just one element. So here are some ideas about the whole space, which is handsome, by the way.

--If you watch TV from the chairs, then layout is fine, but bring pieces in a little closer.

--Room needs more pattern to contrast with dark expanses. Choose a rug with a thick wool pile to bring texture into the room. The palette below (not this rug particularly) would bring warmth into the room and echo your leather sofas--grays, ivory, brownish gold. This rug is from West Elm and has a thick wool pile.

--Coffee table in warm wood finish that echoes floors and leather sofas. It should be large enough to be reachable from each sofa to connect them. Find complementary wood sides tables for each of the armchairs so people have a place to put things down.

Moes Home Dylan Oval Coffee Table Rustic Walnut · More Info

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Magnolia · More Info

--Blank wall: A large semi-abstract landscape artwork across from a window ties the wall and window together.

--Fireplace: Put a basket of birch logs on the hearth and add some to the firebox if you have wood burning fireplace.

Round Seagrass Basket, Large · More Info

--Think about moving TV to the side of fireplace.

River Course Golf Course Home · More Info