The size of the floor grid is too small. Can I revert to the original default size??
Hello @Happy
Your mesh appears to be drastically oversized in the ZBrush worldspace. Use the Tool> Deformation > Unify function to reduce it to the optimal size for working in ZBrush, a Tool> Geometry> Size> XYZ of approximately 2. Meshes that are drastically oversized or undersized in the ZBrush worldpsace may perform poorly. This video explains some, but not all, of the issue that can arise:
Good luck! 