In addition to the question that @Trudy Claspill asked, I’m mulling over what it would take to build and display the creation window…
It’s obviously going to be running Java, so the performance of the JVM is critical. Increasing available application memory might help. I usually recommend two or three dedicated nodes, each with 8GB of RAM with 6GB allowed for Jira. That’s good enough for several hundred developers.
There’s also the Java code cache, which stores compiled code and can lead to slowness if it’s too small.
When you create an issue, Jira will load the screen definition from the database. If the database is slow to respond, you’ll feel that as the create screen loading slowly. This is most likely on shared-tenancy databases, or a (very) poorly performing network connection to the database. If this were the problem, you would have slow performance in other places than just creating issues.
It might be overkill, but an application performance monitoring system like NewRelic can help you quickly narrow down performance problems over time. They have a free tier, but I always worked in places that had the full experience.