Is fech_feed() use lots of server resourses?

Yes it’s true your code can consume more resources then normal.Because you are working with feed and fetch_feed() consume more. It creates SimplePie object based on RSS or Atom feed from URL. You can do one thing just limiting your post as below:

<h2><?php _e( 'Recent news from Some-Other Blog:', 'wpdocs_textdomain' ); ?></h2>

<?php // Get RSS Feed(s)
include_once( ABSPATH . WPINC . '/feed.php' );

// Get a SimplePie feed object from the specified feed source.
$rss = fetch_feed( 'http://example.com/rss/feed/goes/here' );

$maxitems = 0;

if ( ! is_wp_error( $rss ) ) : // Checks that the object is created correctly

    // Figure out how many total items there are, but limit it to 5. 
    $maxitems = $rss->get_item_quantity( 5 ); 

    // Build an array of all the items, starting with element 0 (first element).
    $rss_items = $rss->get_items( 0, $maxitems );

endif;
?>

<ul>
    <?php if ( $maxitems == 0 ) : ?>
        <li><?php _e( 'No items', 'wpdocs_textdomain' ); ?></li>
    <?php else : ?>
        <?php // Loop through each feed item and display each item as a hyperlink. ?>
        <?php foreach ( $rss_items as $item ) : ?>
            <li>
                <a href="https://wordpress.stackexchange.com/questions/227667/<?php echo esc_url( $item->get_permalink() ); ?>"
                    title="<?php printf( __( 'Posted %s', 'wpdocs_textdomain' ), $item->get_date('j F Y | g:i a') ); ?>">
                    <?php echo esc_html( $item->get_title() ); ?>
                </a>
            </li>
        <?php endforeach; ?>
    <?php endif; ?>
</ul>