NWP All Post Types Query

// WP_Query arguments
$args = array(
	'post_type'              => array( 'post', 'collection_unit', 'collection_series_1', 'collection_series_2' ),
	'post_status'            => array( 'publish' ),
	'has_password'           => false,
	'nopaging'               => false,
	'posts_per_page'         => '15',
	'posts_per_archive_page' => '15',
	'ignore_sticky_posts'    => true,
	'cache_results'          => true,
	'update_post_meta_cache' => true,
	'update_post_term_cache' => true,
);

// The Query
$query = new WP_Query( $args );

// The Loop
if ( $query->have_posts() ) {
	while ( $query->have_posts() ) {
		$query->the_post();
		// do something
	}
} else {
	// no posts found
}

// Restore original Post Data
wp_reset_postdata();