Just so you know clearing everything will make the client download everything from the scratch that's why his client become slower after your advise. Clearing cache is not the solution here TBH, your client is running slow a month ago. Lots of players are complaining but you give us nothing but that generic reply of clear your cache and insufficient RAM. Please find a better way.
I understand what you mean, however what you call "generic reply" is the most often solution that helps in those kinds of situations. Sure, it's not a 100% sure cure, but it is one of the most often thing that can fix issues.
That being said, if it doesn't help, I can still try to find more solutions to a problem.