Menu UI Asynchronous Widget
This module improves the performance of node forms by replacing the immediate display of menu selection with a button that loads the full menu UI only when needed. This is particularly beneficial for sites with very large menus.
Inspired by Metatag Asynchronous Widget. This module removes the menu selection UI from node forms and replaces it with a button that loads the full UI if the user wants to add or edit the menu link associated with the node.
In the scenario this module was developed for, two available menus with about 1500 links in each, the performance increase of loading the node form was around 650%.
The impact of using this module will vary depending on your specific setup. If you don't have large menus you will probably not see any performance gains. Instead you will force the user to go through an extra step to add/edit the menu link.
You might also want to take a look at these modules: