Admin Console very slow with large number of realms

With large number of realms the Admin Console takes minutes to refresh the screen after almost any interaction including the initial login.

The reason is slow response of /admin/realms Admin REST endpoint which Admin Console invokes all the time in order to be up-to-date with available realms.

It would most likely be perfectly enough for Admin Console to only retrieve a list of available realm names. Such a resultset would not require a join query which is most likely what is taking time, and should therefore be very fast.