When you view a video on YouTube it automatically selects an HD (high definition) videos. If you have slower connection, you can set YouTube to always play videos of low resolution videos. Here is how :
- Login to your YouTube account.
- In YouTube click on your YouTube username on the top-right.
- Then go to Account Settings → Playback Setup → Video Playback Quality.
- Click on the button Delete Account as shown,
- Choose I have slow connection. Never play higher quality videos.
- Click on Save Changes