Hal,
Your right I think the max for 1080 is 15' but you'll see the cables sold up in 100' plus. You can get a 1080 signal but I would guarantee it wouldn't be reliable. Not sure what the 4k limits are.

Depending what the user is doing we use the Microsoft display adapters, Apple TV's or Firesticks for screen mirroring/sharing with pretty good success and good quatlity