Considering what we know today, and with ammunitions back in stock, there is no reason to carry a 115 grain bullet in a 9mm any more. They have been shown to be inferior in every way possible to 124's and the modern 147's, with some people still thinking 147's are all low power subsonic, when this is no longer the case. 115's tend to turn their energy into temporary cavities and not expand or penetrate deep enough consistently. They seemed like a good idea back in the early days of 20% testing, but the science behind those assertions have been proven false, and all of the theory behind the lighter and faster for caliber has been forgotten in professional circles, remaining as mythology taken as fact in certain shooting communities.
Handguns suffer from low weight bullets and poor sectional densities, which help to cause insufficient penetration and general subpar performance when combined with the low energy in handgun rounds. The heavier bullet, with its superior sectional density and general ability to penetrate and perform against bone, make it a better choice almost universally. Considering almost every single handgun round in common self defense usage is slow, we need to understand that low velocity rounds have always tended to do better with heavier bullets, and that hydrostatic shock is not possible outside the most powerful handguns.
Your 9mm will never be a .30-06, so don't treat it like one. Your ability to kill lies in actual crush cavity rather than any amount of hydrostatic shock or permanent shock cavity, so go with the bullet that will create a better crush cavity, which invariably will favor mid to heavy weight for pistol caliber bullets. Consistent performance, especially in terms of penetration, are important, and a place where light bullets tend to fail.