Gotta spend money to make money. If the goal is just to have 15 "good players", then holding onto all the you guys and never making a move using them is a viable strategy. If the goal is to get two or three blue-chip prospects to put around Aldridge and DeRozan or to get a third star to compliment those guys, then you gotta start distilling the many "good players" into better ones.
As far as your question, I am not sure. I don't know if they can get or who'd they want. Maybe they could get up to 11-13 by combining Poeltl with 19, or maybe they could get 20 straight up for him and then use 20 and 19 to move up. As for who they like, I have no idea. I've never claimed to be in PATFO's head, and I trust that if they like a prospect enough to move up for him that he's worth it.
Trading Poeltl has a lot of benefits. It saves money for next summer, because they would have Milutinov's contract and whatever contract the rookie C has rather than Jakob's cap hold. Assuming Milutinov signs for something like $10M/3, it would reduce the team's cap obligation by $7 Million. That might be enough to open a max slot.
http://www.shamsports.com/capulator?...7578b429853364
That's a rough sketch of what the cap situation could look like next summer with a Poeltl trade.
Roster going into 2020 free agency:
Murray (cap hold)/White
Walker/"Second Round Guard"(Norvell, Herro)
DeRozan/"Second Round Wing"(2020 pick, so no idea)
"Impact Forward" (Hachimura or Reddish)/Metu
Aldridge/Milutinov/"Replacement Center"(Kabengele or Claxton)
Remaining cap space: $32 Million
Room under tax: $64 Million
That's 11 spots already filled with an easy ability to get a few more million to get a full max or to use some of that salary to bring back guys.