flowering 15 plants is alot for a 400 curious as to how big the closet or space is as they dont seem that crowded, suspect you are probably well below the recomended 50 watts per sq ft.
and your light looks like it could be alot closer but pictures can be deceiving would probably lower it as much as you can an air cooled 400 can usually be set about 6 inches above the tops but do the hand test you may not be able to get it that close would expect somewhere between 6-10 inches, this is important during flowering as lights lose half their intensiity for every foot the light has to travel to the plants and ive noticed atleast one other person point this out to you already in this thread.