DecryptStream is very slow about pgpcore HOT 1 OPEN

using PgpCore.Tests;
using System.Diagnostics;

namespace PgpCore.Debug;

internal class Program
{
    static void Main(string[] args)
    {
        TestFactory testFactory = new TestFactory();
        // Generate a 30MB file
        testFactory.Arrange(FileType.GeneratedSmall);
        
        PGP pgp = new PGP();
        pgp.GenerateKey(
            testFactory.PublicKeyFileInfo,
            testFactory.PrivateKeyFileInfo,
            testFactory.UserName,
            testFactory.Password
            );

        EncryptionKeys encryptionKeys = new EncryptionKeys(testFactory.PublicKey, testFactory.PrivateKey, testFactory.Password);
        PGP pgpEncrypt = new PGP(encryptionKeys);

        using (Stream outputFileStream = testFactory.EncryptedContentFileInfo.Create())
            pgpEncrypt.Encrypt(testFactory.ContentStream, outputFileStream);

        // Record time to decrypt
        Stopwatch stopwatch = new Stopwatch();
        stopwatch.Start();
        using (Stream outputFileStream = testFactory.DecryptedContentFileInfo.Create())
            pgpEncrypt.Decrypt(testFactory.EncryptedContentStream, outputFileStream);
        stopwatch.Stop();
        Console.WriteLine($"Decryption using Decrypt took {stopwatch.ElapsedMilliseconds}ms");
        // 3128ms

        // Reset
        testFactory.DecryptedContentFileInfo.Delete();
        stopwatch.Reset();

        stopwatch.Start();
        using (Stream outputFileStream = testFactory.DecryptedContentFileInfo.Create())
            pgpEncrypt.DecryptStream(testFactory.EncryptedContentStream, outputFileStream);
        stopwatch.Stop();
        Console.WriteLine($"Decryption using DecryptStream took {stopwatch.ElapsedMilliseconds}ms");
        // 2406ms
    }
}