title: WPF DataGrid is extremly slow, how can I improve the Initial Loading time?
body: <p>I have a Window with a DataGrid showing grouped Data.</p>
  
  <p>I am loading around 4 x 300 items in the WPF DataGrid which are grouped in 4 groups.</p>
  
  <p>Grouping disables Virtualization.</p>
  
  <p>I set IsAsync="True" so my Window opens fast but the DataGrid is just filled AFTER 11 SECONDS ???</p>
  
  <p>What can I do to speed up the loading/display of my data?</p>