Crushes server on reciprocal connections on big database table?

I’ve happily used Posts2Posts for several years for a connection between my WordPress install’s main post type and a smaller custom post type — works great! But recently, I created a new connection where both sides are the main post type. (It’s to connect two different posts that are translated versions of one another — say, the English and Portuguese versions of the same story.)

function my_translation_connection_types() {
	if ( !function_exists( 'p2p_register_connection_type' ) )
		return;
	p2p_register_connection_type( array( 
		'name' => 'language_to_language',
		'from' => 'post',
		'to' => 'post',
		'reciprocal' => true,
		'title' => 'Translated versions',
		'admin_box' => array(
			'show' => 'any',
			'context' => 'side'
		)
	) );
}
add_action( 'init', 'my_translation_connection_types', 100 );

But when I try to check that connection from a WP template page, it works fine — but over a period of time, the entire site gets extremely slow, MySQL runs super hot, and eventually everything crashes — and then repeat. Server logs and P3 Profiler agree that it’s this Posts2Posts call that is doing it; when I comment out the section below in the template file, the crashing stops.

$connected = new WP_Query( array(
  'connected_type' => 'language_to_language',
  'connected_items' => get_queried_object(),
  'nopaging' => true,
) );

if ( $connected->have_posts() ) :
	echo '<div class="simple-byline-translations"><em>Translation</em>: ';
	$langcounter = 0;
	while ( $connected->have_posts() ) : $connected->the_post(); 
		$transintro = 'Read in English:';
		$langs = get_the_terms( $post->ID, 'intl_languages' );
		if ( $langs && !is_wp_error( $langs ) ) : 
			$langs_links = array();
			foreach ( $langs as $lang ) {		
				if ($lang->slug == 'spanish') { $transintro = 'Leer en español'; }
				if ($lang->slug == 'german') { $transintro = 'Lesen Sie auf Deutsch'; }
				if ($lang->slug == 'chinese') { $transintro = '点击查看本文中文版'; }
				if ($lang->slug == 'portuguese') { $transintro = 'Leia em português'; }
				if ($lang->slug == 'polish') { $transintro = 'Przeczytaj ten artykuł po polsku'; }
				// add more languages here as we publish translations
			}
			$langcounter++;
		endif;
		if ( !$langs ) : 
			$transintro = 'Read in English ';
			$langcounter++;
		endif;	
		?>
	    <a style="color: #333; font-weight: bold;" href="<?php the_permalink(); ?>"><?php if ($langcounter > 1) { echo ' / '; } ?><?php echo $transintro; ?><?php // the_title(); ?></a>
	<?php endwhile;
	echo '</div>';
wp_reset_postdata();
endif;

Admittedly, my wp_posts table is large — 1 GB in size, ~30K rows. But here’s my question: Is this something that is just doomed, running both sides of a Posts2Posts connection on a large database table? Or is there some way I could change this code to make it not melt my server? Thanks!