If you are not partnered with Twitch your viewers are unable to change the quality settings of how they are viewing your stream. This means that if their internet connection cannot keep up with how much data your stream is outputting, they will see a lot of lag and buffering. The best way I have found around this is to keep you bitrate below 2500. (I stream at 2000 @ 720p just fine) anything past 2500 and many of your possible viewers won't be able to watch you and will leave. If you ever do become partnered with Twitch, then you can up your bitrate to the 3500 maximum and your viewers can then adjust their quality settings accordingly.