Will a new submarine cable significantly impact latency?

Hello :)

I'm from Uruguay, and right now two submarine cables connecting Uruguay to Brazil (Tannat) and Brasil to the U.S (Monet) are now active.

The cables are owned by Antel (Uruguayan ISP), Google and other ones I can't remember right now.

So, as far as I know, this will allow Antel and the other owners to don't rely on any other submarine cables when connecting to Brasil and the U.S because they can use their own cables, or even sell its bandwidth.

Well, supposedly the cables are now active, but I didn't notice any significative improvement. I know my internet speed wasn't supposed to change, but I expected a latency improvement.

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So my question is:

• When I'm trying to connect to a server that is in the U.S, How is the shortest/most efficient route calculated?

• Who calculates it? It depends entirely on my ISP?

• I assume the most efficient route is now through that cable... Am I wrong?

• Even if the route changed, and now is going through the cable... Is possible that my latency with that server stays pretty much the same, just for geographical reasons?

Sorry for bad English just in case :) Thanks for reading