Heartbeat API cause Apache/PHP to exhaust memory

[mailandguardian]

WordPress 5.2
Apache/2.4 MPM Prefork (Debian9)
PHP 7.0 Also tried upgrading to PHP 7.2

What you expected to happen:
Apache memory footprint should remain stable.

Steps to reproduce:
Install click-to-deploy-images-wordpress-ha from Google Marketplace.
Upgrade to WordPress 5.2
Import and edit some posts in WordPress Admin
Observe Client side: Examine headers in Chrome Console specifically /wp-admin/admin-ajax.php
Observe Server side on Admin VM : Monitor apache memory with: free -m or htop

Tried:
Upgrading to PHP 7.2.
Tweaks in wp-config.php
define( 'AUTOSAVE_INTERVAL', 600 );
define( 'WP_POST_REVISIONS', false );
define( 'MEDIA_TRASH', true );
define( 'DISABLE_WP_CRON', true );
define( 'WP_MEMORY_LIMIT', '256M' );

[mailandguardian]

Memory Footprint

[SergeyBiryukov]

Related: #26050

[pbearne]

Is this still an issue?