Loading an excessive number of 'test apps' in the beta version of Xcode may at times result in the mentioned error. However, this issue is usually temporary and should rectify itself over time. You need not worry excessively about this problem; instead, continue to experiment and learn.
Even if you try deleting the problematic folder, please note that it will persist in your system's memory and will likely reload when you reopen the Xcode 15 beta. Nonetheless, this behavior is typical of the beta version and does not represent a persistent problem. As you continue to use the software, the loading of your content should gradually improve.