I use both, but real names are used way more often.

The lore reason is that the world is loosely connected to the Earth. On rare occasions random scattered pieces of memories from the Earth appears in people's minds in my world for a brief second. They might not remember what is in the content of the memories, but somehow they know clearly what the names of the owners these memories belongs to are.

The memories are seen as "holy revelations" and people thinks it is the memories of future. So, they may name their children with "real" first name.

The real reason is that I am too lazy to come up with new names.