The Sienna is considerably larger than a Golf. It seats 7 or 8 depending on configuration.

Also remember we use different 20% smaller gallons than you do in Europe. 34 miles per US gallon is about 41 miles per imperial gallon.

https://www.carsized.com/en-us/cars/compare/volkswagen-golf-...

In the same US tests with US spec vehicles, the Sienna actually achieves considerably better fuel economy. Quite impressive given the size difference:

https://fueleconomy.gov/feg/Find.do?action=sbs&id=49303&id=5...