Speed up NMM launch time
From Nexus Wiki
How to Speed up the launch time of NMM if its behaving laggy, dont think its translatable to OBMM or FOMM or WyreBash
If it's taking the program more than 10 or 20 seconds to load, the cause is likely that you have a lot of large mods in the NMM archive folder. I stumbled on a way to speed it up. You can replace the larger archives with empty clones. So, on startup, it sees the clone and assumes that's the original. The reason for this is that it normally goes though a process of loading archive files into temporary memory (I'm not of sure the correct, technical, explanation) based on the sum of their size on disk, for example I've had over 10GB in archives and it's taken up to 2 minutes to start; considering NMM is also a download manager, this means it can take however long before the downloading of mods can begin -- this can be pretty frustrating.
Note: This is best done to large mods you've already installed, or ones you don't plan to install straight away. The empty clones don't cannot be used to uninstall the mods, and need to be replaced again with the original files to uninstall their contents from the Data folder. This is also a good trick to use if you're cloning the game folder and archives are stored there
First, make sure NMM is closed.
Second, make a note of all the archives larger than say 200MB you're comfortable removing.
Third, make a desktop folder, name it something "NMM Clone archives."
Fourth, create two subfolders, one called "Clones", the other "Originals."
Fifth, in the Clones folder create as many subfolders as archives that will need replacing.
Sixth. in the NMM archive folder, highlight the first archive, click again and copy the archive.
Seventh. in the Clones folder highlight and click a subfolder and paste the copied archive there (do it to ensure exact spelling and spacing).
Eighth, deselect and right click it, then archive it using the same format the original has (zip, rar, 7z, etc.).
Ninth, when all the large archives are cloned like this, you can delete the clone folders they were made from.
Tenth, in the NMM archive folder highlight all the originals that were cloned (hold down Ctrl to select multiple files/folders at once) and cut/paste/move them to the "NMM Clone archives/Originals" folder.
Eleventh, move the empty clones to the NMM archive folder.
Twelfth, start up NMM again and check to confirm it's working. If so you will notice it loaded significantly faster. This method is specific to each game's archive list .