How to fix an error when logging into the admin panel?

Question

opencart

There is a site on Opencart 1.5
For two years now everything has been working fine, other sites on Opencart also work fine.
Suddenly, the other day, on one of the sites, when you enter the admin panel (at the entrance), the site literally just hangs. After 5 minutes, the login form opens, I drive in the login and password, it hangs again for 5 minutes. And then it just enters.
Changed admin passwords, ftp password, mysql database password. anyway .....
Where to look for a problem?

Answer 1

I DECIDED ITSELF:
one of the employees of the store turned on "Automatic update of currencies"