Obviously this is a bit late...but for anyone considering this in the future I probably wouldn't recommend it. I also did Interior and Spatial Design with International studies but I had to drop International Studies because the ISDESIGN course was too much. The Interior and Spatial Design course is VERY GOOD and many in the industry (speaking from experience) have their eyes on its graduates so you sort of want to do well. And to do well, you need to dedicate 100% of your spare time (or at least 80%) to doing the assignements.
There's no exams but there's major works due every 2 weeks. The tutors are very demanding too. So unless you're planning to not sleep at all, I'd just stick with the design subject. OR you have the option of doing the International Studies after you finish the design course. But then you'll be in uni for more than 7 years.