Carlos E. R. composed on 2015-11-13 15:03 (UTC+0100):
...for me it is easier to remember ctrl +/-
The font size changes, yes. But the letters are drawn in very thin lines, even if the font size is big.
But it is now much better than it was.
About the thinness, I just saw http://lists.freedesktop.org/archives/fontconfig/2015-November/005594.html and thought I would give it a try after loading
http://fm.no-ip.com/Auth/Font/fonts-comps-oxy.html
on 13.2/KDE3 with default fontconfig AA configuration http://fm.no-ip.com/SS/Fnt/dejavuThin-os132kde3-AA0-1440x0900x096.jpg
and
on 42.1/IceWM with default fontconfig AA configuration http://fm.no-ip.com/SS/Fnt/dejavuThin-os421icewm-AA0-1440x0900x096.jpg
and noticing emaciated looking (thin) DejaVu Sans (and Liberation Sans) compared to the others (Droid, Noto, Oxygen, Roboto). So on 42.1 I renamed /etc/fonts/conf.d/10-* to not be found, and copied from the same PC's Kubuntu 15.10 Wily installation /etc/fonts/conf.d/10-* to 42.1, which produced a striking difference: http://fm.no-ip.com/SS/Fnt/dejavuBuntCfg-os421icewm-AA0-1440x0900x096.jpg
Maybe a similar Ubuntu tweak is worth your trying?