I have and use Thru Paint but its not mapped to fire. It is a large project with a bunch of hi-res textures.
I disabled SimLab FBX Exporter and OBJ Importer, STL Import Export, Super Drape, Texture Resizer, VRay Tools, VoronoiXYZ, Photo Textures, PlayUp, RpWallmaker, Trimble Connect, and Easy Sketch.
My materials and textures were mapping to my AppData location, so it was local but I remapped it to a location where I have all my local libraries.
So far, the lag seems fixed but I have no idea which thing resolved it.