The correct term is one that describes an item exactly.
You have a Block of Fifteen and a Block of Eight.
It looks better when you write the word out instead of using numerals.
They are Not plate blocks because there is no selvage attached (usually on a corner) with a plate number printed on the selvage (margin).
A fair value would be what someone wants to pay for them really. Cayalogue value, you would need a revenue stamp catalogue (not just a stamp catalogue) for Peru, or get an idea from an online dealer in these, or
ebay perhaps, or Delcampe. This is because revenue catalogues are not as common as regular stamp catalohues.