"Cette proposition n'est pas très inquiétante."
Translation:This suggestion is not very worrisome.
Also, in my opinion "worrying" isn't really used in this context. "Worrisome" would be more common.
I came here to say the exact opposite! Google ngrams suggests "worrying" is about 30 times as common.
https://books.google.com/ngrams/graph?content=not+worrying%2Cnot+worrisome&year_start=1800&year_end=2008&corpus=0&smoothing=3&share=&direct_url=t1%3B%2Cnot worrying%3B%2Cc0%3B.t1%3B%2Cnot worrisome%3B%2Cc0
In this case it's a useless metric, since "not worrying" can be used in many more contexts.
Example: not worrying about the future is better for your health.
Not worrisome simply wouldn't work in that phrase.
From what I see, that problem would be solved through asking for "is not worrisome" vs. "is not worrying". In such a case, the numbers indicate that worrying is still more frequent.
"Worrisome", "disquieting", "troubling" have been added. In the negative sense, one would be unlikely to say "not very alarming". The sentence is a mild expression whereas "alarming" is quite exaggerated.