throttle(), clone()

 

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery-throttle-debounce/1.1/jquery.ba-throttle-debounce.min.js" integrity="sha512-JZSo0h5TONFYmyLMqp8k4oPhuo6yNk9mHM+FY50aBjpypfofqtEWsAgRDQm94ImLCzSaHeqNvYuD9382CEn2zw==" crossorigin="anonymous" referrerpolicy="no-referrer"></script>

 

var $window = $(window),
    $header = $('.header'),
    $haderClone = $header.contents().clone(),
    $headerCloneContainer = $('<div class="page-header-clone"></div>'),
    $threshold = $header.offset().top + $header.outerHeight();

$headerCloneContainer.append($haderClone);
$headerCloneContainer.appentTo('body');

$window.scroll($.throttle(1000/15, function(){
    if ($(this).scrollTop() >= $threshold ){
        $headerCloneContainer.addClass('visible');
    } else {
        $headerCloneContainer.removeClass('visible');
    }
}));