Mass PM on Buddyboss / Buddypress: Performance issue

Question

I want to implement an admin-feature to send a direct PM to every user of my Buddypress plattform on specific occasions.

I found the PHP function messages_message_sent already which works great when used like so:

$msg = array(
    'recipients' => [$uid], 
    'content' => $content
);

messages_new_message ($msg);

This is insanely slow - I guess because it actives so many hooks and actions in the system. First I thought the mail notification would cause the delay so I deactivated it:

remove_action( 'messages_message_sent', 'messages_notification_new_message', 10 );

Unfortunately, still I can only send 40 PMs in 1min PHP execution time (on a dedicated 24-cores CPU) - not sure what exactly is causing this delay but it's insane.

Anyone can help and tell me what hooks are irrelevant and/or trigger all that stuff?

I'm now thinking about directly writing in the messages-table in the database directly...