▼ How to check the number of polygons in VRoid Studio
You can check the number of polygons from "Camera / Exporter" > "Export", in the upper right corner of the page.
▼ How to reduce the number of polygons in VRoid Studio
You can reduce the number of polygons by adjusting various parameters in VRoid Studio. You can start with the number of polygons in a model's hair, which tends to have a large number of vertices.
Read the following article for further information.