dynamic dependent dropdown with laravel 5.4 - php

Question

I'm using the dynamic dependent dropdown with laravel 5.4 it works fine in local machine but when I put it on hosting and get accessed by many users it takes too long to get the second dropdown.
Fopm.php:
<div class="form-group col-md-4 col-sm-4 col-xs-6">
{!! Form::label('id_country',trans('Country').":",['class' => 'labels']) !!}
{!! Form::select('id_country',['' => '...'] +$countries->toArray(),Input::get('id_country'),['class' => 'js-example-basic-single form-control select2_country']) !!}
</div>
<div class="form-group col-md-4 col-sm-4 col-xs-6">
{!! Form::label('id_city',trans('City').":",['class' => 'labels']) !!}
{!! Form::select('id_city',['' => '...']+$cities->toArray(),Input::get('id_city'),['class' => 'js-example-basic-single form-control select2_city']) !!}
</div>
script.php:
sw = $('.select2_country').select2({
placeholder: "Sélectionner",
allowClear: true
});
sw.on("change", function (e) {
id = $(this).select2('data')[0].id;
$('.select2_city').val(null).trigger('change');
$('.select2_city').select2({
placeholder: "selectionner",
allowClear: true,
ajax: {
url: '/api/caneva/cities?id=' + id
}
});
});
$('.select2_city').select2({
placeholder: "selectionner",
allowClear: true,
});
Controller.php:
public function cities(SearchRequest $request)
{
$id = $request->input('id');
$city= DB::table('city')->select('libelle_city as text', 'id as id')
->where('id_country', '=', $id)
->get();
return response()->json([
'results' => $city
]);
}