Can I decrease all characters spacing in one go, e.g by 15 on each side?

Hi! Can I decrease all characters` spacing in one go, e.g by 15 on each side? I know there is the grey rectangular shape in the characters box in which I can put my numbers. But where and how can I automatically do it for the entire font? Greetings from Krissel

P.S I am in Glyphs 1.4 Version from June 2014.

Filter > Transform > Metrics