System can be solved by simply buying a larger or faster pump.  Two pumps can be manifolded together to increase system speed.  Before going through this effort the system should be evaluated for leaks. To do this check the ultimate or blank off pressure of the pump.  This is accomplished by attaching a vacuum gauge directly to the pump inlet and letting the pump run for an hour or so.  This reading that is achieved on the gauge is what we refer to as the blank off or ultimate pressure of the pump.  The system should be capable of the same pressure (given some more time).

Leaks are a root cause of system underperformance and fair effort be made to eliminate them from the system.  Not only is system pressure affected by leaks but also the pumps run inefficiently generate oil mist, make more noise and run hotter.   

Also check that any vacuum lines are free and open.  We spent months with a problem when we had a collapsing vacuum hose that we didn't see from the outside it happened internally so try things before going crazy.

Outgassing.  if the system is "wet" then time must allow for ripping out the water.  In ultra high vacuum systems 10-3 10-7 Torr the majority of the time spent pumping down the system is time spent to pump out water vapor.  There are other sources of outgassing just as there are various sources of leaks.