It really depends on what do you mean with performance increase.
You can have an average/max FPS increase with some games even higher than 5%, like SOTR or AC, because their game engines are quite peculiar and the speed is directly proportional to system RAM performances.
Those are the same engines which FPS will increase with better ram latency.
In general most game engines tend to be optimized for a working memory set that fits a 16GB system ram configuration.
Which means that average and max fps is mostly the same with a 16GB or 32GB memory configuration.
Not always, but very often, when the game is CPU bound there's a gap of about 5% or more between the 2 configurations.
The reason is the optimization itself; if you need to keep in check the memory usage you need to swap in and out a lot of data.
When you are CPU bound obviously this swapping is going to be slower cause the rendering pipeline has the maximum priority.
With the current GPUs it's very easy to be CPU limited at 1440p in many if not most games even with a mid/entry-level card.
If you have a good card and an average CPUI then is going to be very easy you'll be CPU bound most of the times.
There are a lot of videos on YouTube comparing 16GB vs 32GB like this one:
You can see which ones give you more avg/max FPS and which ones does not show any improvement.
But you can also see the most important performance gains with more system ram; min FPS and 0.1/1 percentile.
Because all this swapping in and out will likely at some point choke the rendering pipeline.
Which means lower fps at some point, usually when you really don't need it, and stuttering.
What these videos are failing to show is how big is the difference in an average PC.
These tests are ran on similar, clean, Windows installations.
Which is not how most people are using their PC.
Utilities, game panels, antivirus engines, it's pretty common to have a hell of apps running in background.
They all compete together with Windows for a share of the system ram.
When you have only 16GB there's not much left and the stuttering can be massive.
While with 32GB there's usually plenty of ram left for everything else.
Swapping ram to the pagefile is very expensive and if you only have one SSD it's going to compete with the game swapping its data.
Streaming, or just recording the session or the instant replays, it's another use case where only 16GB can kill your fps.
I have an old PC in Italy with an FX-8350 that I use only a few times per year and that one too I upgraded it to 32GB.
Games are on a RAID-5 array, which is just a tad better than an HDD.
Playing from HDD with 16GB was a truly horrible experience, massive stuttering in some games.
The difference with 32GB is like night vs day.
On top of all this Windows itself with every new release is increasing its memory usage.
Starting from 1909 notebooks with 4GB are almost unusable, 2004 is even worse.
I had to do 4 upgrades to 8GB, 2 from HDD to SSD, during last summer between family and friends, due to desperation.
So you have to expect in the next 1-2 years a constant decrease of gaming performances with Windows 10 and only 16GB.