Hello Jan,
The answer is unfortunately no.
Despite software vendors claims IMS-QTI is not a real standard as each LMS has its own "interpretation" of it .
I visited itslearning website and you must understand that sentences like "itslearning users can import content from external vendors directly into the system. They can also export content in IMS format. The IMS Global Learning Consortium develops and promotes the adoption of open technical specifications for interoperable learning technology – and several IMS specifications are now worldwide standards for learning products and services. itslearning conforms to the IMS Content Package, IMS QTI and IMS Enterprise standards."
is just marketing stuff.
Moodle can import questions from Blackboard, Fronter, Canvas (all as some "variations" of IMS-QTI) but not from itslearning.