SPFx Webpart getting loaded with delay

Hi Team,

I am facing some challenges in the loading time of the webpart(15 secs). I was pulling data from the list and binding it to the drop down control in ajax but it has some waiting time since async call is involved.

I need a better performance how this can be achieved. can anyone provide insights.

function getPackingSites()
{
var packagingSiteUrl = siteAbsUrl + "/_api/web/lists/GetByTitle('"+packingSiteList+"')/Items";
var packagingSiteOptions ="";
$.ajax({
url:packagingSiteUrl,
method: "Get",
async: false,
headers: {
"accept": "application/json;odata=verbose",
},
success: function (PackingSiteData) {
if (PackingSiteData.d.results.length > 0) {
for (var i = 0; i < PackingSiteData.d.results.length; i++) {
packagingSiteOptions += "+PackingSiteData.d.results[i].ID+"'>"+PackingSiteData.d.results[i].Title+"";
}
}
},
error: function (x, e) {
alert(e.message.tostring());
}
});
$("#PackingSiteDropdwn").html(packagingSiteOptions);
var tempLink = '+siteAbsUrl+'/pages/Create.aspx?PackSiteID='+$("#PackingSiteDropdwn").val()+'&Source='+siteAbsUrl+'">Submit';
$("#newformSubmitSpan").html(tempLink);
}
}