Orange 3.15 GUI window size issue (Windows 8.1)
This is a known issue: https://github.com/biolab/orange3/issues/3193

It is caused by a bug in Qt 5.9.6 (QTBUG-16252). You should downgrade Qt to 5.9.5.

To do that open the "Orange Command Prompt" from the Window 8.1 'Start Screen' (start menu) and type in conda install qt=5.9.5