Hi @rubao.
I suppose it is possible to correlate low VoLTE MOS levels (from Drive Tests) and high cell utilization (number of users/Volte PRB utilization from counters) especially for cell-busy hour. And then you will be able to identify a kind of threshold when your VoLTE MOS is lower than it is required on a map.
Also you can try to find the most loaded area (just a few sites) and in BH perform drive-tests/walk-tests to accumulate the most relevant information.
I am sure it is possible to correlate low MOS levels with ether counters or DT data (UL SINR/ UL RSSI/ RSRQ and so on).