I primary use my Galaxy S5 as a music hub for my DAC/Amp, and it takes over a minute to delete a folder when I initially connect it to my PC. After the first deletion, the next one is instantaneous.
Even if you haven't deleted a folder already using Opus?
There are general suggestions here (my favorite being to use FTP instead of MTP, which avoids the USB cable, works over wifi, and is a lot more reliable):
(I moved your response into a reply. Please don't edit the original post to replace the whole question, as it makes the thread very confusing for anyone else reading, and also means the change often won't be seen by anyone who already read the thread.)