Parse ~ 1 MB JSON on Android is very slow

I have a file with a size of about 1 MB JSON, which is stored in my resource folder, which I need to upload to my application every time it starts. I find that the built-in JSON parser (org.json) processes the file very slowly, however after analyzing it, I can quickly access and manipulate the data. I counted as much as 7 or 8 seconds from the moment I click on the application until Activity1 appears, but only a few milliseconds to go from Activity1 to Activity2, which depends on the data processed from the data loaded in Activity1.

I read the file in memory and parse it using:

String jsonString = readFileToMemory(myFilename)
JSONArray array = new JSONArray(jsonString);

where readFileToMemory (String) is as follows:

private String readFileToMemory(String filename) {
    StringBuilder data = new StringBuilder();       
    BufferedReader reader = null;
    try {
        InputStream stream = myContext.getAssets().open(filename);
        reader = new BufferedReader(new InputStreamReader(stream, "UTF-8"));
        int result = 0;
        do
        {
            char[] chunk = new char[512];
            result = reader.read(chunk);
            data.append(chunk);
        }
        while(result != -1);

    } catch (FileNotFoundException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    }
    return data.toString();
}

- , ? ?