Sucker Punch did a good job improving on the performance of Infamous Second Son with its prequel, Infamous First Light. They explained how they achieved this effect, and why, unfortunately, these improvements can’t be applied on Second Son.
The improvements were mostly made in the realm of shader optimization. They improved their water ripple compute shader, as well as how g-buffer encodes and decodes normal. They also did not have to worry about the DUP fortifications from Second Son.
The end result was more efficiently produced lighting. This then freed up resources to improve framerate, in the range of three to five frames per second. Digital Foundry explains there are parts of First Light were the improvements are very conspicuous, but otherwise they won’t be that obvious.
As for applying these changes back to Second Son, it is technically possible, but unlikely. Second Son had embedded shaders in the city content. The patch needed to get these improvements in would be 60 percent as big as the game as it is. It is too much work for too little improvement.