The startup launchers for Oxygen XML Editor and its executable internal tools (Tree Editor, XML Schema Regular Expressions Builder, Large File Viewer, SVN Client, Compare Directories, and Compare Files) include a default .vmoptions file that contain some startup parameters (such the -Xmx parameter, which is used for allocating memory for that particular application). You can edit the parameters in these .vmoptions files so that the applications will launch with your desired values. However, if you re-install the application, install an update for the application, or deploy it to other users or machines, those parameters will be reset to their default values.
To be recognized and included, these custom startup parameter files must be saved in the installation directory of Oxygen XML Editor.