Memory means RAM. Space refers to storage, which is your hard drive. They are two entirely different components. With 338 GB of storage space available, the beach balling would most likely be caused by a lack of RAM. If your Mac doesn't have enough RAM installed to handle the OS plus the apps you're using, it has to resort to using disk space as virtual RAM. Disks (and even Solid State Drives) are much slower than RAM.
Using a drive as virtual RAM is known as page outs and page ins. To make room in RAM for an app that is currently being used, other running apps are written to disk in a page out to free up the actual RAM they were using. When the app that was paged is once again accessed by the user, something else has to be paged out to disk and that app read back into RAM (page in). This will result in a lot of beach balls as the OS spends a lot of time writing apps in and out of RAM from or to the drive.
That's the most common reason, though you may have other issues causing such slow downs, such as adware, which eats up system resources every moment your computer is running. Download and run EtreCheck. It is written by long time Apple Discussions member, etresoft. The app purposely avoids collecting any personal data, such as your Mac's serial number, user account name, or anything else that would give the wrong people info they shouldn't have. What is does otherwise collect is your Mac's basic hardware setup (amount of installed RAM, what version of the Mac OS you're running, etc.) and what processes are currently running.
Run the app in standard mode. That is, don't tell it to show running Apple processes. There's lots of them, and we don't need to see those. Copy/paste the results in a new post.
