In 1.15+ the chunkloadevent isn't cancelable anymore. This mechanic is replaced by flagging the chunk as force-loaded.
We need to find the places in code where the following is set and replace the call with the force-loaded flag.

List<Field> fields = plugin.getForceFieldManager().getSourceFieldsInChunk(new ChunkVec(event.getChunk()), FieldFlag.KEEP_CHUNKS_LOADED);

https://github.com/NathanWolf/PreciousStones/blob/master/src/main/java/net/sacredlabyrinth/Phaed/PreciousStones/listeners/PSWorldListener.java#L49

Hi, why do I get this error when I run the latest version of PreciousStones on my server 1.15.1?

[12:41:58] [Server thread/ERROR]: Error occurred while enabling PreciousStones v15.0 (Is it up to date?)
java.lang.NoClassDefFoundError: br/net/fabiozumbi12/RedProtect/Bukkit/RedProtect
at net.sacredlabyrinth.Phaed.PreciousStones.managers.RedProtectManager.(RedProtectManager.java:25) ~[?:?]
at net.sacredlabyrinth.Phaed.PreciousStones.PreciousStones.onEnable(PreciousStones.java:151) ~[?:?]
at org.bukkit.plugin.java.JavaPlugin.setEnabled(JavaPlugin.java:263) ~[spigot-1.15.1.jar:git-Spigot-2ee05fe-d31f05f]
at org.bukkit.plugin.java.JavaPluginLoader.enablePlugin(JavaPluginLoader.java:352) [spigot-1.15.1.jar:git-Spigot-2ee05fe-d31f05f]
at org.bukkit.plugin.SimplePluginManager.enablePlugin(SimplePluginManager.java:417) [spigot-1.15.1.jar:git-Spigot-2ee05fe-d31f05f]
at org.bukkit.craftbukkit.v1_15_R1.CraftServer.enablePlugin(CraftServer.java:462) [spigot-1.15.1.jar:git-Spigot-2ee05fe-d31f05f]
at org.bukkit.craftbukkit.v1_15_R1.CraftServer.enablePlugins(CraftServer.java:376) [spigot-1.15.1.jar:git-Spigot-2ee05fe-d31f05f]
at net.minecraft.server.v1_15_R1.MinecraftServer.a(MinecraftServer.java:456) [spigot-1.15.1.jar:git-Spigot-2ee05fe-d31f05f]
at net.minecraft.server.v1_15_R1.DedicatedServer.init(DedicatedServer.java:266) [spigot-1.15.1.jar:git-Spigot-2ee05fe-d31f05f]
at net.minecraft.server.v1_15_R1.MinecraftServer.run(MinecraftServer.java:783) [spigot-1.15.1.jar:git-Spigot-2ee05fe-d31f05f]
at java.lang.Thread.run(Thread.java:834) [?:?]
Caused by: java.lang.ClassNotFoundException: br.net.fabiozumbi12.RedProtect.Bukkit.RedProtect
at java.net.URLClassLoader.findClass(URLClassLoader.java:471) ~[?:?]
at org.bukkit.plugin.java.PluginClassLoader.findClass(PluginClassLoader.java:135) ~[spigot-1.15.1.jar:git-Spigot-2ee05fe-d31f05f]
at org.bukkit.plugin.java.PluginClassLoader.findClass(PluginClassLoader.java:81) ~[spigot-1.15.1.jar:git-Spigot-2ee05fe-d31f05f]
at java.lang.ClassLoader.loadClass(ClassLoader.java:588) ~[?:?]
at java.lang.ClassLoader.loadClass(ClassLoader.java:521) ~[?:?]
... 11 more

This Plugin requires RedProtect in your plugin folder.

What? why now you have to add the plugin?

Never used this plugin. I just updated it to the latest version. PR changes into it if you want to make it optional.