Hello, admin-ajax.php is something needed for wordpress to work fine. But you can disable the heartbeat of wordpress to make it load faster. This may help you https://wordpress.org/plugins/heartbeat-control/
To speed your wordpress, use
– W3 Total Cache guide http://code.tutsplus.com/tutorials/configuring-w3-total-cache-general-settings-i–cms-20920
DO NOT ENABLE MINIFY
– Use a CDN ( Cloudflare, MAXCDN…)
– Use “Remove query strings from static resources” plugin
– Use an image optimizer plugin like Smush it
– Use a Lazy load plugin
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