As you have already read in this guide, the new 1.14 versions' general performance is much worse than in previous versions. According to some reports and our own tests, the performance of 1.14 improves significantly if they have set a reduced render distance.
For this reason, all Vanilla 1.14+ servers have a reduced default render distance. You can change this in the server.properties.
We recommend switching to the PaperMC server software to improve performance.