Hi, I found your original post here: How to stop real-time changes polling in issues and merge-requests pages?
Unfortunately, it’s only available to change at server level, so for your own installation: Polling interval multiplier | GitLab
It cannot be changed on gitlab.com since you are not the admin of gitlab.com. If you are looking for it to be implemented on gitlab.com then it would be better to open an issue here about it: Issues · GitLab.org / GitLab · GitLab since Gitlab devs do not frequent the forums, and concentrate with issues that have been opened on the Gitlab project itself.
By opening an issue, means other people can vote on it, and the more interest that is seen, the more chance of it being implemented. Whether it is possible for it to be done on a project level or group level though remains to be seen, but that would only come about once an issue has been opened for it.