Before all, you need to set exactly your POV, height, distance etc. Then you create the rectangle with the texture on it and push pull it. Then you move and rotate it to be parallel with your POV and at the same height. Then you intersect the walls with it and you take the sample paint and select that texture which should be projected. Then you paint the walls.
Now if you go in Parallel mode it looks great, but we as humans can't see in parallel mode. Now you get back to your Pow and adjust the line on the distant wall so that they meet with the ones from the closer wall.
Now you make the applied distant wall texture a unique texture and you go and edit that in an external editor so that it follows the lines.
Hope it makes sense.