Many large companies still use IE11, and maybe It will take a long time to migrate to Chrome. and because of speed issues, I don't think JIRA is the right solution.

For reference, we have successfully used Jira in 6.X, but we are getting a lot of complaints about speed issues in IE11 after install 8.X. so Teams using the 6.x version succeeded in applying Jira, but teams using 8.x are failing. (Each team is about 1000-10000 people)

I think, maybe..  that as of release 7.10, it changed to a new look, resulting in loads of css and js. From this point on, it started to slow down in IE.

It is necessary to optimize the speed of css rendering in IE11 by adding options such as Classic theme mode.