What could be the reason for the long script processing in the Wordpress admin panel (nginx php-fpm)?

Question

PHP

The problem is the following. When updating user data in the WordPress admin panel, the script runs for a very long time, there was a problem with a 502 time-out error, set fastcgi_read_timeout 150, everything works, but for a very long time. On LAN, on normal Denver, everything works fine. On the cloud there is a bunch of nginx + php-fpm + opcache + selective memcached under ubuntu. The site flies, but there is a problem with this.
I give part of the nginx setup, if you don’t judge strictly, I’m trying the whole thing for the first time.

location / {
    try_files $uri $uri/ /index.php?$args;
}
location ~ [^/]\.php(/|$) {
  fastcgi_split_path_info ^(.+?\.php)(/.*)$;
  if (!-f $document_root$fastcgi_script_name) {
    return 404;
  }

  # Backend server
  fastcgi_pass unix:/var/run/php5-fpm.sock;
    
  include fastcgi_params;
  fastcgi_index index.php;
        fastcgi_read_timeout 150;
    
  fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name;
  fastcgi_param QUERY_STRING    $query_string;
}

Thank you!
UPD: Thanks to the advice, I saw that the problem is in the long TTFB

Answer 1

Thank you very much for the thought process of dimasmagadan and Ninja Mate .
So, after I went looking for the reason for the long TTFB, I came across serverfault.com/questions/350062/the-strange-case-...
on the advice I also turned on slowlog php-fpm which showed that the problem is in mail() php in the handler , as a result, I checked the work of sendmail and it turned out that it was he who sent letters for a minute. I went to ect/hosts and changed the settings as described here https://brianhogg.com/how-to-fix-slow-sendmail-on-...
Everything worked!

Answer 2

why do you think that it is php that slows down?
Can you enable the slow mysql query log on the server?