From what I've seen over the years the stock speakers (for any brand, unless it's a Bose system) are around 90db sensitivity, usually. I went over to Crutchfield wanted to see what they had for a 2015 Fusion.. I picked the big screen without the Sony logo on the radio, then I picked just the regular radio setup and found same speakers..Unless it's different for the Sony logo'd stock headunit.. The speakers I found.. Actually I have these, Rockford Fosgate Prime Series. They are awesome! Have them with the factory radio powering them. Plenty loud!
They are a 6.75" speaker and 91db sensitivity. The tweeter is NOT overpowering, so if you wanted to use your factory tweeter or upgrade to something the fits well in the factory opening, I don't think it would be too "bright" sounding.
Here's a link,
https://www.crutchfield.com/p_575R1675X2/Rockford-Fosgate-R1675X2.html?tp=105