php/mysqli select strange high CPU usages

Hi php friends,

I'll be very thankful to hear your opinion my php problem:

I have a php website with mysql database with 1 table with about 20,000 rows.

My code looks like this:

$mysqli = new mysqli($mysql_hostname, $mysql_user, $mysql_password, $mysql_database);
if ($mysqli->connect_errno) {
    exit();
}

if ($stmt = $mysqli->prepare('SELECT title, description, content FROM '.$tableName.' WHERE slug=?')) {
    $stmt->bind_param("s", $slug);
    $stmt->execute();
    $stmt->bind_result($title, $description, $content);
    $stmt->fetch();
    $stmt->close();
}

$mysqli->close();

...

/* just visualize the read variable above */

<h1><?php echo $title; ?></h1>

<?php echo $content; ?>

The problem is that in the hosting statistic, there's really huge php CPU usage, i.e. for yesterday the statistic is:

PHP CPU usage is 144 min.

MySQL CPU usage is 2 min.

I try to find the problem for more than a week, I'll be very, very thankful for your help

Thanks in advance for any reply!