What were the specs of the server and which Spigot fork did you run?
A month ago I ran a Paper instance from a Digital Ocean instance with about 4 GB of RAM and OpenJ9 JVM and it never dipped below 20 TPS even with a larger render distance. This was on Vanilla 1.17.
Have you noticed much difference between a HotSpot-driven JRE and OpenJ9?
I am somewhat irrationally biased against J9 because they made us stick it in everything at IBM, but I'm willing to reconsider for better Minecraft performance.
I have yet to see hard data on it, but the folks that have been in the trenches doing client-side mods on Minecraft swear that J9 is the superior JVM for the latest versions of Minecraft (1.16+). I don't know that anyone has really done a proper benchmark.
