In addition to what Ken said, it's probably not that Opus is slower at reading the directory listings (almost all programs read them in the same way) but that some of your columns are causing Opus to open all the files to inspect them and that is clogging up the network.
The Description column is often an unexpected cause of file access (since all the plugins may look inside the file to see if they can generate a description), as is any other column which causes Opus to read the actual data out of files. Turn on the Network Drives folder format and give it a minimal set of columns (e.g. just Name, Size, Date.)
Also, make sure you have automatic folder size calculation turned off (this can also be done via the Network Drives folder format) as if it is on it will cause all of the subdirectories to be read in, which will slow things down. (The calculation is done on a background thread so it is normally not an issue but over a slow network it can clog up the request to change directories enough that things appear sluggish.)
Finally, the Total File Count and simlar columns, which count the number of files in sub-folders, also cause sub-folders to be enumerated and should generally be avoided on network drives.
In addition to the essential Folder Formats FAQ which Ken already mentioned, you may find the FAQ on folder-size auto-calculation useful: