Here are some best practices to assure your trigger evaluation step is as quick as possible:
-Turn off any trigger campaigns that are no longer needed. (This will reduce the # of active monitors that will cause evaluations to fire off for a trigger event)
-Note: Once a quarter, Marketo will find smart campaigns that have sat dormant (no people trigger it) for 6 months or more and deactivate them automatically. However you can manually deactivate campaigns on your own.
-Convert Trigger campaigns to Batch if they are not needed for immediate response (for activities or campaigns that can run nightly). Batch campaigns run on a separate component of Marketo's processors which doesn't affect the Trigger qualifier speeds.
Each instance's situation can be unique. Our support team would be glad to go over best practices for your instance and also review how you can self-maintain the campaign deactivation through the Campaign Inspector.