There is no built in way in BabylonJS to measure total number of vertices so here we go

gistfile1.txt

// TODO check for instanced, should we exclude them from count?
// TODO check for invisible

let verticesCounted = 0;
let indicesCounted = 0;

export function totalVertices(scene: Scene): { vertices: number; indices: number; } {
    verticesCounted = 0;
    scene.meshes.forEach((mesh) => {
        if (mesh) {
            countVertices(mesh as Mesh);
        }
    });
    return {
        vertices: verticesCounted,
        indices: indicesCounted,
    };
}

function countVertices(mesh: Mesh) {
    if (mesh.getChildMeshes) {
        const children = mesh.getChildMeshes(true);
        children.forEach(countVertices);
    }
    if (mesh.getTotalVertices && mesh.getTotalIndices) {
        verticesCounted += mesh.getTotalVertices();
        indicesCounted += mesh.getTotalIndices();
    }
}