You want a newly planted tree to provide screening 15 to 20 feet off the ground?!!! No

matter how much money you have this is not a realistic goal. The largest tree you could reasonably plant will still take ages to do screening at that height. Like, plan on 10 years. Put a fence on the deck with lattice or whatever and cal it a day. Or put a serious planter with evergreens on the deck.

Is the deck in your yard or your neighbors? Here’s where a picture is worth a thousand words!

neighbor's deck...lol no not expecting that much screening right away. Thinking long term. Some of the trees I'm looking at grow three feet a year but then I need them to stop! will post a pic tomorrow

Ok will wait for picture . Also tell us where you live - closest large city. Need to know climate to make any kind of planting suggestions.