I believe this will be better in LyX 2.2.0. You are welcome to try our latest test version. You can download the windows installer here:
ftp://ftp.lyx.org/pub/lyx/devel/lyx-2.2/2.2.0-latest
Note that it is just a development version. If you have any feedback (positive or negative), please send it to
lyx-devel@lists.lyx.org
If that doesn't improve things, it might be because our Windows installer isn't using Qt 5 yet. Qt 5 has many advantages for HiDPI displays. Our next pre-release will likely use Qt 5.5.1 for Windows.