Quote from LastLuck "we're currently on 1.14.4 We'll try to update it to the newest mc versions. But that has not our priority yet. It's always a mess with the plugins, cuz not every plugin is ready for the next version of mc"
1.15 isnt a stable version yet. We waited to update to 1.14.4 (final 1.14 version) until the release of 1.15 this ensures us that the final version of 1.14 is stable. Minecraft wont release 1.16 until 1.15 is stable. So we wont upgrade to the next version until there is a stable build of 1.15 aka the final build.
Although upgrading will unlock a lot of cool additions for us it also has its downside. Plugins all need to get updated to 1.15 wich is easier said then done since a lot of the mechanic are created by ourself or they are highly customizeble plugin wich can create a lot of issues.
Eventually I dont see us upgrading to a new version until they add a big gamechanger (ne blocks, mobs, etc)