Hello,
If your commands/code for the Model 2000 is performing as you require, you can also use the Model 2000 Emulation command set (Menu > System Settings > Command Set) to allow the DMM6500 to act as a drop-in replacement until you develop new code designed for the DMM6500.
However, if you would like to optimize commands for the DMM6500, it seems that you should only need to add an NPLC designation to make a significant impact on the speed of your measurements.
There are several settings that we typically recommend reviewing/modifying to optimize speed vs accuracy (filter, manual range, etc), but NPLC tends to be the largest contributor.
You can find more about this SCPI command on page 12-99 of the Reference Manual:
https://www.tek.com/en/tektronix-and-keithley-digital-multimeter/dmm6500-manual/model-dmm6500-6-1-2-digit-multimeter-3
If you are looking to initiate your measurements (number defined the the SENSE:COUNT command) and then report the latest, you can use the :MEAS? command.
If you only want to take a single initiated measurement and report that latest reading, you can use the :READ? command.
If you want to take multiple readings and report them all, you can use :INIT then :TRACE:DATA? commands.
Please review these commands and required arguments for each in the manual linked above.
Since you are using a filter, there will be some delay time to collect all of the averaged readings and calculate the appropriate reporting value.
These filters can dramatically impact speed and total measurement time.
Overall, total test time and reading speed will depend on several factors and filters can contribute to this depending on their configuration.