I have jarred honey that is 18% and so far it is fine... but I also sold about 4, 5 gal buckets.. In order to bring the moisture content down, I put it in a sealed room with a dehumidifier, with a fan blowing to circulate the air in the room... In two weeks THAT honey went from 19.5 to around 17% moisture using the refractometer.. it worked well.. it didnt crystalize so I didnt have to heat it.
I had the honey in the bottling tank and two 5 gal buckets. So about ten gal was in the bottling tank. All had the tops off with screens over them.