Why is the Dial by name so SLOW to identify someone?

When calling in and getting the auto attendant, using the dial by name option, it takes the system about 5 or 6 seconds between when you input the letters of the name to when it suggests a name. 5 seconds of dead air is long enough so you wonder if the system is still responding. It is far too long and I have had two complaints from incoming callers so far. They say are unsure if the system is responding.