From Ross-Tech Wiki

4.8 How can I speed up my sample rate in VAG-COM?
The sample rate at which you can view and log data is largely determined by each controller in the car. There are a few things you can do to speed up the rate for a given controller. First, logging one group at a time, rather than two or three, will help greatly. In order to get the highest sample rate possible go to the Options screen and set Blk Int to 25 and Char Int to 0. Note, however, that this may cause unreliable communications with some controllers. The KP2 Time parameter only applies to controllers using the KWP-2000 protocol. Decreasing it speeds up the sample rate in Measuring Blocks on control modules that use the KWP-2000 protocols. Try setting it to 0. If any of these adjustments cause unreliable communications, change them back closer to the defaults. If in doubt, use the Restore Defaults button!
In Engine controllers using KWP-2000, there is a [Turbo] button in the latest version of VAG-COM. This can significantly speed up sampling, in some cases to over 30 samples per second. See the Measuring Blocks page for more information.