Change postgresql encoding

I have a new postgresql installation done, it has utf-8 encoding.

I have to make a Oracle database migration and it has ISO8859-15 encoding, should I change postgresql encoding to same Oracle encoding or with utf-8 it should go well?

If I want change postgresql encoding, I have understood that I should reinstall postgresql (I do installation from rpm official binary files for red hat), someone knows say me if when you install software it asks you for choosing encoding or it puts it from what you have in the system? (I did installation from many time ago and I don't remember it).

Thanks beforehand.

P.D.: I've tried change encoding to a new postgresql database to latin9, but it gives me error for having utf-8. 

Regards...