Profiling a simple scenario:

$ ~/Install/jdk9u20/bin/java -jar dist/nashorn.jar -Dnashorn.typeInfo.disabled=false --class-cache-size=0 --persistent-code-cache=false -scripting --log=time test/script/basic/compile-octane.js -- --iterations 5

...yields a few simple low-hanging fruits, here is one of them. Out of 320 seconds of run, and 38 seconds spent in class installation time, ~13 seconds are spent here:

12.690 jdk.nashorn.internal.codegen.CompilationPhase$12.transform(jdk.nashorn.internal.codegen.Compiler, jdk.nashorn.internal.codegen.Compiler$CompilationPhases, jdk.nashorn.internal.ir.FunctionNode)
5.220 jdk.nashorn.internal.runtime.Context$ContextCodeInstaller.initialize(java.util.Collection, jdk.nashorn.internal.runtime.Source, java.lang.Object[])
...
5.170 jdk.nashorn.internal.runtime.Context$ContextCodeInstaller$1.accept(java.lang.Class)
5.170 java.security.AccessController.doPrivileged(java.security.PrivilegedExceptionAction)
5.120 jdk.nashorn.internal.runtime.Context$ContextCodeInstaller$1$1.run()
5.000 java.lang.Class.getDeclaredField(java.lang.String)
4.940 java.lang.Class.privateGetDeclaredFields(boolean)
4.920 java.lang.Class.getDeclaredFields0(boolean)
4.890 JVM_GetClassDeclaredFields
4.610 InstanceKlass::link_class(Thread*)
4.770 InstanceKlass::link_class_impl(instanceKlassHandle,bool,Thread*)
3.700 Verifier::verify(instanceKlassHandle,Verifier::Mode,bool,Thread*)
3.630 ClassVerifier::verify_method(methodHandle,Thread*)

Update: See updated stack trace, it seems like the first call to getDeclaredFields causes the class to initialize and link. We spend the largest slob of time verifying the incoming bytecode.