1. Hell's Kitchen is NYC's 20th Precinct, not the 15th.
2. Where's Avenger's Tower?
It does bother me they never work Avengers Tower into the skyline. It can't be that hard or cost that much money to render. You can't tell me they don't have some stock references or images they could throw in there at Marvel Television or whatever FX houses they sub-contract.
Composite the images!Most of the views of New York are with actors in them, so stock references wouldn't work. These aren't generic establishing shots of New York. If they did use movie footage for the generic establishing shots, it would be internally inconsistent if they didn't use it elsewhere.
I too would prefer to see Avengers Tower. But I also have never made a major production involving CGI and don't know how much time and effort is necessary. I don't think they're ignorant of Avengers Tower. They made a decision it wasn't worth the effort.
The second one is a budget issue. They devoted money to other things.
When did they say it was the 15th Precinct? There might be reasons for doing it - it's not a real precinct, so they aren't going to offend any real people or because it's a tribute to NYPD Blue. I just don't remember any precinct specifically mentioned.
The NYPD has this policy that real precinct numbers cannot be used in works of fiction, because they don't want people to confuse actors in cop costumes with real police officers. This is the reason that the NYPD and the Boston Police Department among others create police cars with fictional precinct/district numbers.