HTTP/2 has a great feature called server push. It enables the server to send multiple responses in parallel for one request. In a blogpost on the Symfony Finland blog Jani Tarvainen demonstrates how to make use of server push with the Symfony Kernel.

$app->get('/images'), function () use ($app) {
    $images = array('/images/1.jpg','/images/2.jpg','/images/3.jpg');
    $response = new JsonResponse($images);
    foreach($images as $image){
        $response->headers->set('link','<' . $image . '>; rel=preload; as=image',false);
    }

    return $response;

Read the entire article for some more background info.