A. Where a structure, use of land, use of a structure, or use of structures and land in combination exists in the flood fringe district or floodway district on the effective date hereof that would not otherwise be permitted under the provisions hereof, such structure or use may be continued so long as it remains lawful, subject to the provisions of sections 15.7.3, 15.7.4 and 15.7.5 of this chapter.