Performance of scrolling and editing is diminished when Track changes are enabled.  Issue seems to be related to RevisionsToolTipLayer and occurs when more than a couple of paragraphs are inserted in the same revision.

Workaround: remove the UI layer responsible for tooltips of revisions.

    [CustomUILayersBuilder]
    public class CustomLayersBuilder : UILayersBuilder
    {
        protected override void BuildUILayersOverride(IUILayerContainer uiLayerContainer)
        {
            uiLayerContainer.UILayers.Remove(DefaultUILayers.ToolTipLayer);
        }
    }