Hi Yunan. I just want to add that, if you use "virtual scrolling", your grouping will not work as expected, if you set virtual scrolling you must use paging, and your "grouping" will only be applied on the "current" page, so your group totals will be inexact, and you will not see groups from other pages! That solution is almost unusable (enable grouping + enable virtual scroll)
We also noticed some performance issues in IE also (the latest IE in Win10), cpu goes up to 20% on a I7 when scrolling! I didn't compare with oldest version of kendo to see if there's a difference... We use frozen, grouping, ... looks like we're using the grid the same way!