Lag will always be a thing with vanilla severs, especially one as populated as ours. It's why we have rules like the entity limit (100 or fewer). Controlling entities is one o the easiest ways to reduce lag. Watch your entities (E:#/# in the f3 menu), clean your grinders, keep animal farms small, pick your items up, try to refrain from using armor stands and item frames because they count as entities. There are a number o other ways, but there are many ways to reduce your entities