> I believe a finely crafted native code solution for this problem could achieve x3 less ram usage and x2-3 indexing/search performance

Many people believe that about everything written in Java. The story often ends up a lot more complicated though. In the domains where it shines Java is surprisingly hard to beat without very significant effort. And then you must also contemplate what they same significant effort would achieve if directed at the Java solution or cherry picking particular performance hotspots out of it.