What can slow down a site with Ajax?

Question

Yii

Hello!
Not long ago, I noticed that the site somehow works slowly with an Ajax request ... it didn’t exist before and didn’t touch the codes for a long time ...
so there is a search for cargo by number ... when a request is made to the server, the answer will return in 3 4 seconds ...
and even tried to return an empty answer in the code... it's still so slow... what could be the problem?

By the way, everything is fine on LAN...and there are other sites on this hosting too...they are also all right...