select all the pages and "apply Master to Pages" in the pages pane menu
Fede, thanks for your input. I am affraid that it would be more complicated than that. I am talking about 15 Indesign documents, structured in a Indesign book file. Therefore, the master-pages would need to apply to different documents, as batch, based on page layout (single page or DPS).
Sorry for not being clear, English is not my first language.