1.15.2 Huge TPS Problems

I am having TPS problems with my 1.15.2 server and I can’t seem to find the reason. I have about 25-30 players on my server. The PC has 16 GB RAM and my CPU is:
Intel® Xeon® CPU E5-2690 0 @ 2.90GHz (4 CPus), ~2.9Ghz (I know it isn’t the best)
Also this is the timings result
https://timings.aikar.co/?id=b18992061aba41d6b135c6037a3dd7ea
Please help me

While looking at the Timings, I noticed that the TPS Drop came, when a sudden increase in loaded entities and chunks happened. I would reccommend to check that first, not that someone purposefully built a lagmachine.