For whom it may concern:
I had the same problem (on 0.9.2 / LDAP / FreeBSD Jail), and after some debugging it turned out to wait a lot on the line
This function (or to be precise, the socket.gethostbyaddr(name) function) stook ages (15-20 seconds) in my setup.
The reason for it was that my upstream ISP had made changes and misconfigured PTR entry for the mailserver hostname.
Once the PTR record was up and correct again, the Dashboard speed was fine again.
Usually when setting up a mailserver it is obvious to have a correct reverse entry for the domain, but just in case someone runs into the same problem, or sets up iredmail before setting up DNS:
Make sure that your reverse DNS entry is correct and accessible for the mailserver before setting up iRedAdmin.
Best is to test your PTR, e.g. with
host 188.8.131.52 # (ip of your mailserver)
directly within a shell of the iredmail server.
Note: supposedly you could run into the same delay if ...
the hostname of the iredmail server is not the FQDN (for example in a DMZ, with an internal address). In this case the internal name should be resolvable forward and backward. or
/etc/resolv.conf is not configured correctly... or
the nameserver in /etc/resolv.conf is not accessible (firewall) or offline..