just a general idea. Instead of creating a category for each event (which can grow a lot over time and not everyone has the permission to create new categories) I would suggest to consider tags instead.
Tags also have the advantage that you can apply multiple. So FOSDEM could be tagged as “FOSDEM”, “2019”, “brussels” for example and CLT as “CLT”, “2019”, “germany”. This way you can also easily search for all events in 2019, for all the FOSDEM plannings over the years, for all events in your country, etc.
What do you think?