Hi, 
The relation 15820539 is not correct ... 
Please read https://wiki.openstreetmap.org/wiki/Relation:multipolygon#Multipolygon_created_by_only_one_polygon
Bsicly there needs to be an outer area ... and then inner areas - All of these are simple closed ways .. then make the relation. https://wiki.openstreetmap.org/wiki/Relation:multipolygon#iD