I wrote my last post before your recent reply.
Most plants prefer to be tightly potted and grow best when they are. Roots coming out of drain holes is not a good reason to repot. When you do repot, it is important to use a pot with drain holes. For future reference, keep the plant in its plastic pot and set that pot inside a more decorative ceramic planter like the one you used. Double-potting leaves the roots undisturbed and makes watering much easier.
Large pots and fertilizer do NOT make plants grow bigger except in very limited circumstances. The repotting will actually retard growth somewhat. Stop fertilizing. You can spray the leaves if you want, but it does not really benefit the plant in any significant way.
It does not sound like that location will provide adequate light. Peace Lilies do prefer low light, but that simply means just beyond the reach of the direct rays of the sun, usually within 3-5 feet of a very sunny window or even closer to a north window.
Because it is in a sealed planter, you have to be very careful not to overwater. Ideally, you water only just as or before the leaves start to wilt. Then, add just enough water so that it almost reaches the wilting point in about a week. You will have to experiment a bit to determine the right amount of water. The roots need oxygen as much as they need water and they get oxygen only when the soil is allowed to dry out a bit.
