Android - Retrofit is slow compared to the python script

I'm using Retrofit2 on my Android app but I'm experiencing a lot of slowness in calls compared to the same calls made through a Python script. The Android smartphone and the pc running the script use the same internet connection.

For example, a GET call (406 byte) takes on average the following times:

• Android App: 525ms
• Python script: 111ms
• Safari: 109ms

The first GET call (3140 byte) has the biggest difference:

• Android App: 1723ms
• Python script or Safari: 294ms

My Retrofit API Class code:

    import java.util.concurrent.TimeUnit;

    import okhttp3.OkHttpClient;
    import okhttp3.logging.HttpLoggingInterceptor;
    import retrofit2.Retrofit;
    import retrofit2.converter.gson.GsonConverterFactory;

    class APIClient {

        private static Retrofit retrofit = null;
        private static String url = "http://test.mylink.com";

        static Retrofit getClient() {

            HttpLoggingInterceptor interceptor = new HttpLoggingInterceptor();
            interceptor.setLevel(HttpLoggingInterceptor.Level.BODY);
            OkHttpClient client = new OkHttpClient.Builder()
                                    .readTimeout(60, TimeUnit.SECONDS)
                                    .connectTimeout(60, TimeUnit.SECONDS)
                                    .addInterceptor(interceptor).build();

            retrofit = new Retrofit.Builder()
                    .baseUrl(url)
                    .addConverterFactory(GsonConverterFactory.create())
                    .client(client)
                    .build();

            return retrofit;
        }

    }

API calls are made inside a thread

class TestClass extends Thread {
     ...
     public void makeCall() {
            Call<Proof> call1 = _apiInterface.getProof();
            call1.enqueue(new Callback<Proof>() {
                @Override
                public void onResponse(Call<Proof> call, Response<Proof> response) {
                    ...
                }

                @Override
                public void onFailure(Call<Proof> call, Throwable t) {
                    call.cancel();
                    ...
                }
            });
     }
}

Has anyone had a similar problem with Retrofit?