I recently upgraded my graphics card from a GeForce GTX 660 to a GTX 970. Upon installing the new card, all lines in SketchUp became heavily aliased. I did not change any settings in the driver or in SketchUp. The NVidia driver is the newest version. I already found a topic on almost this exact same problem (New card and SU15 and all of a sudden I have jagged lines) and it did not offer any solution. If I put the old graphics card back in, the jagged lines go away.
Here are some images, for comparison: