Efficiently get all results from Google Datastore and return as JSON

I have a project currently running Laravel 5.7.

I have a bunch of IoT sensors that are sending data into Google Datastore.

I am wanting to query this data so that I can show a graph of this data on the frontend of my app.

The frontend makes a request to my project, my project makes the request to Google Datastore, and then builds up the result to return it as JSON to the frontend.

There's a fair bit of data (currently 1200 rows), and it takes about 17 seconds to fetch and render on the screen. Which is longer than I would like.

Here is my current code to fetch this IoT Data:

public function fetchData()
{
    dump("GDS query starting " . date("Y-m-d H:i:s"));
    $query = $this->datastore->query()
        ->kind('IotEvent')
        ->filter('device_id', '=', 'abc123')
        ->filter('published_at', '>=', '2018-09-19T04:52:01.429Z')
        ->order('published_at', Query::ORDER_ASCENDING)
        ->projection(['current_temperature', 'target_temperature', 'published_at']);

    $results = $this->datastore->runQuery($query);
    dump("GDS query finished " . date("Y-m-d H:i:s"));

    return($this->transformData($results));
}

private function transformData($results)
{
    dump("GDS transform starting " . date("Y-m-d H:i:s"));

    $data = [];

    foreach ($results as $result) {
        array_push($data, $result->get());
    }

    dump("GDS transform finished " . date("Y-m-d H:i:s"));

    return $data;
}

According to the dump()s the request to Datastore is done within a second. But looping over each row, getting the values, and pushing them to the array takes 14 seconds.

I can't seem to find any method on $result that will allow me to pull out all the results, and no documentation seems to hint that a method like this exists.

On this GitHub issue they hint at using iterator_to_array() which I have never heard of before. However, using it like below just returns me a bunch of empty JSON objects on my frontend:

private function transformData($results)
{
    dump("GDS transform starting " . date("Y-m-d H:i:s"));

    $data = iterator_to_array($results, false);

    dump("GDS transform finished " . date("Y-m-d H:i:s"));

    return $data;
}

Is there a method to make this process a lot quicker, or anything I can do to optimise the current process of looping each row? Once in production, each request to fetch data can be expected to return around 5000 rows, so 5 times what I am currently fetching.

I am using the official Google Datastore Library.