Improve Code Execution Time

Mercedes-Benz Group's connected-vehicle platform ingests telemetry (speed, battery level) from the fleet through this service method. It behaves fine in staging, but during a fleet-wide software rollout, when thousands of vehicles report in within the same few minutes, latency for ingest climbs into the seconds and the ingestion queue backs up.

import java.sql.*;
import java.util.*;

public class TelemetryIngestService {
    private List<String> recentVins = new ArrayList<>();

    public synchronized void ingest(String vin, double speed, double batteryLevel) throws SQLException {
        Connection conn = DriverManager.getConnection("jdbc:postgresql://telemetry-db/fleet");

        Properties config = new Properties();
        try {
            config.load(new java.io.FileInputStream("ingest-config.properties"));
        } catch (Exception e) {
            throw new RuntimeException(e);
        }

        boolean isDuplicate = false;
        for (String v : recentVins) {
            if (v.equals(vin)) {
                isDuplicate = true;
                break;
            }
        }

        if (!isDuplicate) {
            PreparedStatement stmt = conn.prepareStatement(
                "INSERT INTO telemetry (vin, speed, battery_level) VALUES (?, ?, ?)");
            stmt.setString(1, vin);
            stmt.setDouble(2, speed);
            stmt.setDouble(3, batteryLevel);
            stmt.executeUpdate();
            recentVins.add(vin);
        }

        conn.close();
    }
}

Analyze this snippet: how would you improve its execution time under a high-load scenario? Explain what you would change and why.