I recently upgraded my ubuntu linux to 15.04. Some of the places icon size is too big after upgrade. I have attached some images below.
There is a fix for FS icons on this link How to fix huge FS Icons in Ubuntu 15.04 menubars?
I have tried with FS icons and it works for me, fixing the issue you report and also the huge icons in menus and titles. It did not fix other icon sets though :-(