Typically we see an increase of factor 3-5 in execution times when the same test is run on Selenium Box vs. a SaaS solution. This is because Selenium Box runs inside your network and is close to the rest of the CI / test infrastructure. Latencies are minimized and hence the significant increase in speed.
Background: Selenium / WebDriver is an HTTP based protocol which requires a roundtrip from the client -> server -> browser -> application under test and back for each command. When running on SaaS solutions the browser is running outside of the customer network with potentially large latencies in between.