The first thing you need to do is open Task Manager and check what's running in the background when you're not using anything. A lot of times these AI tools leave processes active, indexing, syncing, or updates that eat up your resources even after you close the app. There you'll see exactly how much RAM and CPU each thing is using, and that's way more reliable than any number someone tells you.
Real consumption depends a lot on what tool you're using and how you have it set up. Copilot alone shouldn't hog a ton of RAM, but if you're running local models or have things like Windows Search with aggressive indexing turned on, that does weigh on it. Also check if you don't have a bunch of browser extensions running - those definitely eat up memory. Sometimes the slowness comes more from that than from the AI itself.
My concrete recommendation: go into Task Manager, the "Processes" tab, and sort by memory and CPU. Write down which processes are using the most and google the ones you don't recognize. Also check the "Startup" tab - disable everything you don't need launching with Windows. It's probably one or two things eating up resources for nothing. If it's still slow after cleaning that up, then yeah your machine might actually need more physical RAM, but generally that's not the case.