I'm opening another issue to this same problem since it is happening again with our users.
Previous issue: JRA-31581

We have several customers that collect "common hours" such as vacations and meetings on the same issue for all employees. This means that the history of these issues grows very big (thousands of changes).
We have noticed that adding hours to these issues takes a good deal longer than adding hours to "new" issues (5-10 seconds, sometimes longer). We have tried both the standard "Log work" function and Tempo with the same results.
Experimenting a bit also shows that it looks like the "dispatchEvent" parameter to the "createWorklog" function is the key. Setting the "dispatchEvent" to false makes everything OK. This means that somebody that is listening to the ISSUE_WORKLOGGED_ID event is taking a long time processing.
Note that we disabled all plugins except the Atlassian plugins (see attached screenshot) which means that it's either JIRA itself or some of the listed Atlassian plugins that is the culprit.