If a theme, that is five or six long answers relating in some way each other, were to include, say, walls; one would expect to see at least five or six W's in the long answers [walnuts, wall hangings, wall banger, walleye, wallpaper]. But in this puzzle, W's were not endemic to the theme. Nevertheless, there were six W's used in this grid. Now W's are not among the most used letters in our language, so to see as many as there were in this grid is unusual. I'll bet in the next hundred 15x15 grids you will not find as many "unrelated" W's. (But now, because I said it, there might be one next week.)
This is not a qualitative observation, and I would love to see a puzzle with 20 W's, though perhaps not all editors would agree.
I hope this helps.