Hi Themis,
Jpeg compression is good, but you need to set a proper setting.
The best ratio quality / size is obtained around 85%
Below 80% the quality decreases for ridiculous size saving, and above, the size drastically increases without an obvious gain of quality.
It should be better if you can change it in hoversnap.
Otherwise, you can take screenshots with FSscreen, and use a freeware like xnview to batch convert the bitmaps to jpegs with a very good quality compression.