How has the 15 to 12 RD rule change affected history?

Many classic fights would have different outcomes.

Joe Louis losses to Billy Conn, and maybe Joe Walcott 1.

Rocky Marciano also looses to Walcott in the first fight.

You could say Joe Walcott stock goes up, Mariano stock goes down a bit and Joe Louis stock slides the most. And this is just a small sample.

For modern fighters, you could argue the durable types with a lot of stamina who lost decisions in 12 rounds where their opponent was running out of steam might have drawn or won had it been 15.

I prefer 15 rounds, and even think boxing would be better off with 13 round title fights to avoid draws / bad calls from the judges.