I have a flat floor that is out of level 1/2" over 16 feet. Should I be concerned, I can notice it now against the gyprock, no trim yet. Should I use a leveling agent.

2nd part of the question I Ditra on the floor before noticing it. Ditra says to level first then Ditra, how much of an infraction would it be to add the leveler over the ditra.

Mant tks in advance for assistance

I personally, would leave it alone. Since the floor is flat, you won't notice the run...especially after you are all finished with your project. Lately, the floors I've been working on, have been out 1/2 inch in 2 feet, so I'm a little envious.