buildHealth.jelly asks for both job.buildHealth and job.buildHealthReports, causing Job/Folder.getBuildHealthReports to be called twice just to render a single table cell. I would guess that the performance problem comes in the first call, and the second call is mostly working off a hot cache, but if you are under memory pressure it is always possible that garbage collection has to run between the two calls and so work is wasted. I see no need to call job.buildHealth; should suffice to assume that the implementation is simply going to be to look up the first element in job.buildHealthReports (as it is in both Job and Folder).
Worse, sometimes job.buildHealthReports is called a third time.