With more information from your system, it's impossible to give advice.
Once your system is up and running, open a terminal window and do ...
$ uname -a <enter>
... and then do ...
$ eeprom <enter>
Copy the results back here.
There are a few things that may benefit from a minor change or two.
There are some OBP functions that exist during POST, however,
that are essential critical functions and just cannot be turned "off".
Ever.
Well, for that platform, you can only change the diagnostic settings
to what could be described as "quick", or "normal".Not much else.
Here's the OBP 3.x Command Reference Manual
http://docs.sun.com/app/docs/doc/806-1377-10?q=openboot+command+reference
( Docs.Sun.Com can sometimes be a slow site, be patient bringing that link up )
Review it for decriptions on diagnostic level, diag-switch, and debug modes.
I anticipate they're already at minimal levels on your box
and you've simply found that the Enterprise systems have a long POST.
After all, they're a design from the mid-90's.