Generosity in debates about reformed senate (15)

'generosity' is the definition.
(being considerate of other people)

'in debates about reformed senate' is the wordplay.
'in' is an insertion indicator.
'debates' becomes 'considers' ('consider' can be a synonym of 'debate').
'about' becomes 'a' (abbreviation in Chambers).
'reformed senate' becomes 'tenes' (I can't explain this - if you can you should believe this answer much more).
'a'+'tenes'='atenes'
'considers' enclosing 'atenes' is 'CONSIDERATENESS'.