List<CIBSubjectData> list1 = .....

list1.forEach(data ->
     merge(data)
);

for (CIBSubjectData data : list1) {
    merge(data);
}

public class Warmup {
    static int dummy;

    static void merge(String s) {
        dummy += s.length();
        dummy++;
        dummy -= s.length();
    }

    public static void main(String[] args) throws IOException {
        List<String> list1 = new ArrayList<>();
        Random rand = new Random(1);

        for (int i = 0; i < 100_000; i++) {
            list1.add(Long.toString(rand.nextLong()));
        }

        // this will boostrap the bytecode instrumentation
        // Stream.of("foo".toCharArray()).forEach(System.out::println);
        long start = System.nanoTime();
        list1.forEach(data -> merge(data));

        long end = System.nanoTime();
        System.out.printf("duration: %d%n", end - start);
        System.out.println(dummy);
    }
}

duration: 71694425

duration: 7516086