spring-data-cassandra-reactive improve performance of ReactiveCrudRepository.save

I have simple showcase with ReactiveCrudRepository, which shows almost 2x difference in insertion speed using ReactiveCrudRepository.save() vs ReactiveCqlOperations.execute()

Here is the code:

Entity:

@Table("snapshot")
@Value
@Builder
@EqualsAndHashCode(callSuper = false)
@RequiredArgsConstructor
public class SnapshotRecord {

    @PrimaryKeyColumn(ordinal = 0, type = PrimaryKeyType.PARTITIONED)
    long id;
    @PrimaryKeyColumn(ordinal = 1, type = PrimaryKeyType.PARTITIONED)
    short market;
    @PrimaryKeyColumn(ordinal = 3, type = PrimaryKeyType.CLUSTERED)
    Instant slot;

    double value;
}

Repository:

public interface SnapshotRepository extends ReactiveCrudRepository<SnapshotRecord, Long> {

    default Mono<Boolean> saveViaCql(ReactiveCqlOperations cqlOps, SnapshotRecord record) {
        return cqlOps.execute(
                "INSERT INTO snapshot (id, market,slot,value) VALUES (?,?,?,?) USING TIMESTAMP ?;",
                ps -> {
                    return ps.bind(
                            record.getId(),
                            record.getMarket(),
                            record.getSlot(),
                            record.getValue(),
                            record.getSlot().toEpochMilli() * 1000
                    );
                }
        );
    }
}

Runner:

Flux<SnapshotRecord> data = Flux.generate(Object::new, (state, sink) -> {
            ThreadLocalRandom random = ThreadLocalRandom.current();
            sink.next(
                new SnapshotRecord(
                    random.nextLong(),
                    (short) random.nextInt(),
                    Clock.systemUTC().instant(),
                    random.nextDouble()
                )
            );
            return state;
        });
        subscription = data
//.flatMap((SnapshotRecord record) -> repository.saveViaCql(cqlOps, record), 512, 2048)
.flatMap(repository::save, 512, 2048) //doing this runs almost 2x slower than previous line
            .doOnNext(d -> success.incrementAndGet())
            .onErrorContinue((throwable, object) -> fail.incrementAndGet())
            .subscribe();

Full project link on Github:

https://github.com/piddubnyi/spring-data-cassandra-performnace

Is there any way to improve insertion performance of repository.save(), or spring-proxy is really costly in this case?