Great quiz! Might want to set the timer a bit lower though. With 25 minutes it's easy to get to a point where you can just run through all the world's capitals to guess your way to 100%. Still though, worth a nomination in my book :)
15 minutes is still probably too long - most people who know all the capital cities will easily fancy themselves to type every entry in this time. I would say 8 minutes is enough time to think but not long enough to guess every answer.
The United Kingdom had control zones in both these cities after WWII, though both cities were only partly British, so I guess it’s up to you.