I am working on a project for myself whereby I am trying to search users within the WordPress database based on postcode/zip and radius but the code which I'm using takes forever to load and results in a timeout error even though there are only about 200 users. I am quite stumped by this so I am hoping someone out there can lead me in the right direction. Here is the code I have currently:

                $url = "=".urlencode($_GET['postcode'])."&sensor=false&key=MY-API-KEY";
            $result_string = file_get_contents($url);
            $result = json_decode($result_string, true);

            if(!empty($result['results'])){
                $orig_lat = $result['results'][0]['geometry']['location']['lat'];
                $orig_lon = $result['results'][0]['geometry']['location']['lng'];

            }


            $center_lat = $orig_lat; //insert the lat of where you are
            $center_lng = $orig_lon; //insert the lng of where you are
            $radius = $_SESSION['postcode_radius']; //insert the radius of KM that you want to search

            $multiplier=3959; //miles
            $multiplier=($multiplier*1.609344); //use km instead

            $users = get_users( array( 'fields' => array( 'ID' ) ) );

            //now we got all our users that have latitude (i assume they also have longitude ^^)
            $nearbyusers = array();
            foreach($users as $user){
                      $lat = get_user_meta($user->ID,'lat',TRUE); //assuming the user latitude is a meta field named "latitude"
                      $lng = get_user_meta($user->ID,'lng',TRUE); //assuming the user longitude is a meta field named "longitude"
                      $distance = ( $multiplier * acos( cos( deg2rad($center_lat) ) * cos( deg2rad( $lat ) ) * cos( deg2rad( $lng ) - deg2rad($center_lng) ) + sin( deg2rad($center_lat) ) * sin( deg2rad( $lat ) ) ) );
                      if($distance<$radius) {
                          $nearbyusers[] = $user;
                      }
            }
            print_r($nearbyusers);

Any ideas on this and why it doesn't work as expected?

Thanks!