This is an example of a Google Data Studio dashboard embedded in this web page.
And this is an example of an embedded Tableau dashboard.
It does appear that the Tableau dashboard may load slightly faster than the GOogle Data Studio dashboard. Test this yourself though to see how they perform for you. The Google Data Studio dashboard is reporting lve data from a Google Analytics data source updated on every load, whereas the Tablea dashboard is only presenting a static data source. This is not the fairest of tests and it may be worthwhile experiementing with other parameters. Both dashboards though do appear to load reasonably well.