As other members have said, we are currently using 1.13 for the server and are using software/add ons to allow backwards compatability for future versions (1.14+). Currently the tech team is working on updating to 1.15.2 (skipping 1.14) however our aims at the moment is adding features first and then updating so we then don't have to add them later.
There has been progress on some of our core plugins and we are already looking for and bundling together external plugins that have been updated already. The main wait though for updating is some of our closed source plugins. As exciting as it is, we ask for your patience as unfortunately, it is going to take a bit of time.
Hope this helps