In addition to what the sibling reply said. There is also the issue of your choice of runtimes. Java has the slowest startup time and Go the fastest. C# is faster than Java but still slower than Python and Node.
Clever uses of dependency injection without reflection (think dagger not spring) and reducing code size as much as possible can give you fairly fast cold start times with a Java execution environment. Bloated classpaths and reflection filled code will destroy your initialization time.