One thing you could check is whether or not XMP is enabled in the BIOS (hint - it should be enabled).
With RAM, as with other computer hardware, it's the law of diminishing returns - you could upgrade to 32GB of 3600MHz RAM and you might see a performance increase but if your system is bottlenecking elsewhere, your mileage may vary.
Best thing to do for starters therefore is to benchmark your system as it currently stands and then work from there - this site is pretty good (and free) https://www.userbenchmark.com/Software
It will score each of your components (RAM, CPU, GPU, HDDs etc) against a baseline and you can then use that to inform your decision about what to upgrade first.