Jira issue creation process running slow

Hello, I’m working on a Jira on-premises plugin using the Atlassian SDK. This plugin will allow user to create issues in Jira based on data received via third-party APIs. I’m using a for loop to iterate over the data and sequentially creating Jira issues.

I started the process for approximately 125000 data in order to evaluate the functionality. But as time passes, the process slows down. I started the process at 11:40 AM, and in 20 minutes it generated about 11000 issues. Then, in an hour, it generated about 22000 issues, but after that, the number of issues generated per hour decreased.
below is report generated in jira which shows count of issues created every hour
I have a Jira instance running on a virtual machine, and when I started this process, no other processes were active. I am unable to figure out the problem; can someone please help to identify what might be issue?

I also checked the response time for issue creation in Jira, which is initially around 900-1500 ms and as time passes it goes upto 5000ms.