Yes Tom is not me, but he knows his Norway spruce. And so does Ken. Norway spruce retain their lower branches very well, unless in fairly dense shade.
I think your 15 foot spacing will work very well. If I wanted to have perfect spacing for a row of "specimen" 60 year-old Norway spruce, I would recommend wider spacing, maybe somewhere between 20 and 30 feet (there is no "absolute" perfect spacing). But given your situation and goals there for a screen, 15 feet will do just fine. As they grow rather large, they will tend to grow together and the trees will not be so broad as they would be if given more space, but I see no problem. Enjoy!
Of course, if some grow faster, and look better than others, the weaker, less beautiful ones can be thinned out later, and that can give more room to the nicer, stronger ones. But that would most likely lead to some irregular spacing. You can decide what you would like when the time comes.
--spruce
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cabinets & floors
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