Server lagging so much without a single player online/1 - 2 players online [Fabric]

[NotFlow69]

i hosted my smp with this tutorial and sometimes the server crashes without a single player online, im using fabric a very, VERY low amount of mods, i have edited the startup file for ram and so on but the server is lagging so much that aternos is better, PLEASE HELP ME!!!! @lordofwizard @DumbCaveSpider