Hi Yu,
Thanks for your interest in Syncfusion products.
We would like to let you know that we can use some optimization techniques to improve the performance of the GridGrouping control. You can refer the Performance Demo available in the dashboard location for the optimizing the grid when large data is been loaded. You can refer the below location for the sample.
Location:
<Installed Location>\Syncfusion\EssentialStudio\<Installed Version>\Windows\Grid.Grouping.Windows\Samples\Performance\Engine Optimization Demo\
Please let us know if you need further assistance.
Regards,
Anish