If you can only focus for 15m at a time, then work on increasing that naturally.
Make yourself a timer app that will increase your work time by N every day before sounding an alarm, then browse/do whatever. When you come back you restart it and do another block.
As other people said, it's the possibility of interruptions that break your concentration. I'm working in game dev (Unity specifically), and it's really good at breaking your concentration. It'll take a long time to compile, randomly crash or take time importing things etc, which then makes you want to not sit there and watch it.
Make yourself a timer app that will increase your work time by N every day before sounding an alarm, then browse/do whatever. When you come back you restart it and do another block.
As other people said, it's the possibility of interruptions that break your concentration. I'm working in game dev (Unity specifically), and it's really good at breaking your concentration. It'll take a long time to compile, randomly crash or take time importing things etc, which then makes you want to not sit there and watch it.