yes, autocomplete, than typing 2-3 letters. Also you first thouth right - if you will make request via ajax to standart query for all posts - it will not reduce the number of requests, but it will improve the page loading time with requesting heavy query async. Also for now, I have reduced my admin page load time from 30s to 6s (it's localhost, prod server more better) with simple construction:
$all_products = [];
$args = array(
'posts_per_page' => -1,
'post_type' => 'product'
);
$query = new WP_Query( $args );
if ( $query->have_posts() ):
while ( $query->have_posts() ): $query->the_post();
$all_products[get_the_ID()] = get_the_title();
endwhile;
endif;
and then
array(
'id' => 'order_products',
'type' => 'group',
'clone' => true,
'sort_clone' => true,
'collapsible' => true,
'save_state' => true,
'default_state'=> 'collapsed',
'group_title' => array( 'field' => 'product_id' ),
'add_button' => 'Добавить товар',
'fields' => array(
array(
'name' => 'Товар',
'id' => 'product_id',
'type' => 'select_advanced',
'options' => $all_products,
'class' => 'product_id'
),
.
