Still really difficult to tell what it is from here, but my money is with you on leaf septoria. You're approaching the point where it's not a good idea to defoliate any leaves. If you want to get rid of the sick leaves, you could do it now, all at once. But you don't have much foliage, so I would recommend leaving as much leaf as possible.
Throughout flowering you can remove 1-2 leaves every couple of days without giving the plants too much shock. I think you should just monitor how the disease progresses, removing leaves in intervals if it starts looking really bad.
Let's hope for the best :)