NVZ Features takes more time to draw on map

[ShivamMishra2]

I am fetching data from Layer: NVZ_2017_Combined_Waters_Final_Designations
I am using arcgis javascript api 4.14 version
If I zoom in the map on zoom level 6 then only this NVZ features are displaying on map, but its taking more time to load on map.

Here is my code: 

var map;
require([
"esri/widgets/Sketch",
"esri/Map",
"esri/layers/GraphicsLayer",
"esri/views/MapView",
"esri/geometry/Polygon",
"esri/layers/FeatureLayer",
"esri/symbols/SimpleLineSymbol",
"esri/Graphic",
"esri/symbols/SimpleFillSymbol",
"esri/Color"
],
function(Sketch, Map, GraphicsLayer, MapView, Polygon, FeatureLayer, SimpleLineSymbol, Graphic, SimpleFillSymbol, Color) {
const layer = new GraphicsLayer();
const map = new Map({
basemap: "streets",
layers: [layer]
});

const view = new MapView({
container: "map",
map: map,
zoom: 5,
center: [-3.118092, 54.509865]
});

// set dynamic url for feature layer
function initOperationalLayer() {
var featureLayer = new FeatureLayer("https://environment.data.gov.uk/arcgis/rest/services/EA/NitrateVulnerableZones2017Final/FeatureServer/0",{
mode: FeatureLayer.MODE_ONDEMAND,
map.add(featureLayer);
}
}
initOperationalLayer();
);

I have attached the video: