The vast majority of games work just fine with 16gb RAM. I recommend running your higher speed modules as dual-channel and selling/repurposing your previous hardware.
Unless they are the same brand and specification, patchwork RAM tends to have compatibility issues leading to software hanging and potential crashes. YMMV.
ETA: Honestly you’re more bottlenecked by your CPU. I’d recommend finding a used Zen2 chip if you can, such as the Ryzen 5 3600. I have a 3600x in my home desktop with a basic Coolermaster dry tower. I’ve never gone over 70°F/~21°C on fairly high settings of TW:3K. That should speak enough of Zen2’s performance.
chef’s kiss~ My friend, you are a wordsmith.