The "real reciprocity" of Foma 200 is so abominable that you might want to avoid long exposures with it entirely. You'd have to make a tabulation for every different contrast filter you might use, because the respective filter factors themselves shift at long exposure times, especially if a red filter is used. That is one of the reasons why a simple answer can't be given.

In my experience, Foma 200 really was an outlier in terms of being way more unpredictable than other films at longer exposures, really anything longer than a second. But if you're only talking about 8 to 15 seconds overall, you might be able to juggle that OK.