In case the "Capture Video Log" option is enabled in the global Error Handling tab (Control Desk > Settings) or in the Error Handling of a particular Process, a Process that runs through a Robot can run much slower.
Have in mind that a Process that performs internal calculations, normally runs extremely fast when executed through a Robot (and not the Process Designer). When video log is enabled, it is trying to capture each and every one of the steps of the Process. Hence, this causes the whole machine to slow down (CPU utilization may reach 100%). As a result, the Process runs slower as well.
There is no workaraound for the above, so in case the Process execution speed is of high importance, it is suggested that you enable the video log only for some of the Processes that do not include a lot of internal calculations and not globally.