CreateGroundFromHeightMap VERY SLOW movement

When using CreateGroundFromHeightmap... When i use the camera to move around on ground IS VERY SLOW and VERY CHOPPY... AND LOWERS FPS down to 15fps.

This is my code for creating Ground:

            // Parse scene native mesh and heightmap terrains
            var terrains:BABYLON.Mesh[] = this._scene.getMeshesByTags("[TERRAIN]");
            if (terrains != null) {
                terrains.forEach((terrain)=>{
                    console.log(terrain.metadata);
                    if (terrain.metadata != null && terrain.metadata.properties != null) {
                        if (terrain.metadata.properties.heightmapBase64) {
                            var tempBase64:string = terrain.metadata.properties.heightmapBase64;
                            var terrainWidth:number = terrain.metadata.properties.width;
                            var terrainLength:number = terrain.metadata.properties.length;
                            var terrainHeight:number = terrain.metadata.properties.height;
                            var minimumHeightLevel:number = terrain.metadata.properties.minimumHeightLevel;
                            var maximumHeightLevel:number = terrain.metadata.properties.maximumHeightLevel;
                            var groundTessellation:number = terrain.metadata.properties.groundTessellation;
                            var surfaceMaterialId:string = terrain.metadata.properties.surfaceMaterialId;
                            var surfaceMaterialInst:BABYLON.Material = null;
                            if (surfaceMaterialId != null && surfaceMaterialId !== "") {
                                var material:BABYLON.Material = this._scene.getMaterialByID(surfaceMaterialId);
                                surfaceMaterialInst = material;
                            }
                            BABYLON.MeshBuilder.CreateGroundFromHeightMap((terrain.name + "_Mesh"), tempBase64, {
                                width: terrainWidth,
                                height: terrainLength,
                                subdivisions: groundTessellation,
                                minHeight: minimumHeightLevel,
                                maxHeight: maximumHeightLevel,
                                updatable: true,
                                onReady: (mesh:BABYLON.Mesh) => {
                                    mesh.parent = terrain;
                                    mesh.scaling = terrain.scaling.clone();
                                    mesh.position.x -= terrain.position.x;
                                    mesh.position.z -= terrain.position.z;
                                    mesh.checkCollisions = true;
                                    if (surfaceMaterialInst != null) {
                                        mesh.material = surfaceMaterialInst;
                                    }
                                }
                            }, this._scene);
                        } else {
                            // TODO: Native Mesh - Note should try do all c# editor side
                        }
                    }
                });
            }

Any help would be awesome... as always