Moisture content for thick shelf

15% moisture isn't even at EMC for air drying lumber outside let alone inside. It'll take about a full seasonal cycle indoors at 70 degrees and 30-50% seasonal humidity before that 2.5" thick slab finally gets close to EMC and settles down and quits moving on you. Just remember, wood is a slow moving sponge that wants to reach equilibrium with its environment. If you take KD wood that is 6-8% and put it out in your nonheated/climate controlled garage, it will swell right back up to 11-13%.