Android - Updating TextView causes lag on Bluetooth

Question

I have created an application that sends data via Bluetooth. The application sends the corresponding seekBar value once it has been changed then updates the text view with a special value calculated from that seekBar value.

The problem is that there is a lag during the Bluetooth communication. I've determined that the lag comes from the update event of the textView:

public void onProgressChanged(SeekBar seekBar, int progress, boolean fromUser) {
    if(fromUser) {
        switch (seekBar.getId()) {
            case R.id.seek_bar_vario:
                if (progress < 100) {
                    seekBarVarioDim.setProgressDrawable(getResources().getDrawable(R.drawable.warm_white_progress));
                    seekBarVarioDim.setThumb(getResources().getDrawable(R.drawable.warm_white_thumb));
                } else if (progress > 150) {
                    seekBarVarioDim.setProgressDrawable(getResources().getDrawable(R.drawable.cool_white_progress));
                    seekBarVarioDim.setThumb(getResources().getDrawable(R.drawable.cool_white_thumb));
                } else {
                    seekBarVarioDim.setProgressDrawable(getResources().getDrawable(R.drawable.netural_white_progress));
                    seekBarVarioDim.setThumb(getResources().getDrawable(R.drawable.netural_white_thumb));
                }

                varioLighting.setMessage(Constants.MESSAGE_NOP_ID);
                varioLighting.setWarmWhiteRatio(255 - progress);
                varioLighting.setCoolWhiteRatio(progress);
                sendData(varioLighting.getStateMessage());
                mVarioKelvin = 3000 + (int)(progress * 12);//11.76470588f);

                //THE FOLLOWING LINE CAUSES THE LAG:
                textViewVarioKelvinAndIntensity.setText(mVarioKelvin + "K - " + mVarioIntensity + "%");


                break;
            case R.id.seek_bar_vario_dim:

                varioLighting.setMessage(Constants.MESSAGE_NOP_ID);
                varioLighting.setIntensity(seekBarVarioDim.getProgress());
                sendData(varioLighting.getStateMessage());
                mVarioIntensity = (progress * 100) / 255;

                //THE FOLLOWING LINE CAUSES THE LAG:
                textViewVarioKelvinAndIntensity.setText(mVarioKelvin + "K - " + (mVarioIntensity) + "%");


                break; 
        }
    }
}

Even if I update the textView with a constant one-char string (e.g. "K"), it still causes the lag. If I remove that line(s) it works as I expected.

So, what can be the problem. And what should I do to fix that problem?