While adjusting screen resolution and/or text size can solve the problem, I'd like to point out that there are inconsistencies between QGIS tools. Some tools will display at high res, while others are only readable at lower res. Here are two examples taken from a Microsoft Surface Book, 3000 X 2000 resolution screen, text size 200% (recommended), QGIS 2.14.2. At this setting the Spatial Query tool displayed correctly:
However, at the same display settings, the Select by Location tool is unreadable and unusable (although it will display correctly at 1920 X 1080, text size 100%):
Perhaps the fine people that create these tools could modify their code to work correctly with the higher resolution screens that are becoming more common!