Ken paints 3 tiles/minute + 2 tiles/minute = <<3+2=5>>5 tiles/minute.
Laura can paint 5 tiles/minute x 2 = <<5*2=10>>10 tiles/minute.
Kim can paint 10 tiles/minute - 3 tiles/minute = <<10-3=7>>7 tiles/minute.
All 4 can paint 3 tiles/minute + 5 tiles/minute + 10 tiles/minute + 7 tiles/minute = 25 tiles/minute.
In 15 minutes, they can paint 15 minutes x 25 tiles/minute = <<15*25=375>>375 tiles.
#### 375