What led to the passage of the 15th amendment was the rising discrimination between different racial, sex, and social groups within the united states. It was ratified during the first or second reconstruction after the civil war, it granted blacks to vote along with women and foreign immigrants. another reason was due to the KKK, the Black codes, the Jim Crow laws, along with the rising "red scare" or the threat of communism in america at the time.
The advantages was to make these individuals feel safer and more free when exercise their basic human rights, but it also meant more votes in elections. Another advantage was to help stop discrimination.
I hope this helps! : )