I haven't changed any setting, I just updated to 1.5.5, so therefore:

1. wpForo Spam Control is enabled. -- It was and it still is.

2. user is New (under hard spam control) during first X posts option's value is not 0. -- It was always 1 (one) and it still is.

3. also, I'd recommend increasing spam suspicion levels... -- It is irrelevant with regards to "New user hard spam control". Hard spam control should work regardless of what the suspicion levels are. That's why it's "hard".