I think that picture might need to be lowered so it is more eye level. It's hard to get a feel for the room, do you have any more pictures??

I agree that the picture needs to be 'eye level'. Since you have a blank wall and are moving things around - what do you have that will fill it up? A big mirror? A collage of small prints? Another large landscape? Since your ceiling height is 15', you could paint the ceiling to bring it 'down'. Or move the landscape picture, (with some sconces perhaps), to the large blank wall and wallpaper or faux paint to add interest.

Yes, I definitely think the picture needs to come down. In all honesty, though, I don't think that picture really works there for some reason. If you're going to leave it there, I'd get maybe a different colored frame or paint that one-- a richer color. I think the pretty blues in the pics look kind of washed out right now because of the light-colored frame.

I love your high ceilings! I'd LOVE to have celings that high!

First, I would love to see the wall below the border painted in one of the medium tones in the border paper. It would help break up the height of the space a bit.

I think the wall where you have the art would be better served by a collection of three shelves on which you could place some decorative things, perhaps lean a piece of art, etc. One lone piece of art on the big wall may not have enough texture and interest to really break up the flat feeling of the empty space. However, if you want to keep the framed piece, it needs to be lowered so that the center of the art is at eye level. Hanging the art high doesn't solve the high ceiling issue.

A narrow vase in the corner where the banjo top meets the wall filled with some twigs and greenery would be nice, and would break up the expanse of mirror a bit.

Pick an accent color like a blue or green for your towels, rug, etc..