One of the cool things about XTOL is supposed to be that you can mix it at room temperature, unlike D76 and others.
When I used XTOL I had the same problem, and after awhile I stopped worrying about a little undissolved chemistry swirling around the bottom of the mixing vessel. I would always pour the solution into another container, careful not to let the sinkers (as opposed to floaters! transfer over. Honestly, I never saw a difference in development based on fully dissolved or partially dissolved chemistry. Once or twice I did see some dense spots where a particle would stick to the film, but then I started pouring from the mixing vessel to something else to stop that.
Bottom line...unless huge portions of the chemicals are not dissolving, I don't think you have to worry about it.