In Inkscape Preferences > Interface are controls for changing the icon size. But I seem to recall certain situations where those controls don't work very well. You could try searching the forum for more info. I'm pretty sure this is where I've seen other messages about the icon size. The screenshot...

Couldn't figure out how to customize the toolbox icon size. I am using a high resolution screen (3200X1800). the tool icons and menu are are too small. Any clue of how I can increase their size will be appreciated. The attachment shows how my screen currently looks.