To manipulate rendering settings please take a look at OccViewer.RenderingParams. Here you can switch to on/off shadows, set shadow map resolution, background color. Manipulations with some of these parameters can give better picture quality and worse performance or vice versa.
Example of usage:
// increasing of resolution scale gives better picture quality, but affects performance
OccViewerModule.renderingParams.renderResolutionScale = 2;
// increasing of shadow map resolution increases shadow quality, but decreases a performance
OccViewerModule.renderingParams.shadowMapResolution = 4096;