A first simple check: restart the system, open the task manager / resource monitor to monitor the use of RAM, then launch Photoshop and try using the tool giving you some problems for monitoring the use of RAM.
Do you see a peak of using 100% of the RAM? – If this is the case, more RAM can solve the problem. If you do not use 100% of the ram, the problem is elsewhere. [Such as a badly configured setup that isn’t making effective use of the GPU. More tricky sources of slow downs like this come from things like not enough processor level cache]