Do you know if you have installed anything not inside the multiverses yet? Mine was very snappy until I attempted to add the cairo-dock plus all the svg libraries for it. It hasn't been the same since. I love the Slab like Linux Mint Menu but I haven't found a good way to get it back to its original responsive self.
I tried to right click > Preferences to get into the Configuration Editor. Under MintMenu>Plugins>applications I cranked down category_hover_delay to 1. That works well the first time it pops up, but when loading other categories it again chokes.
Maybe its just an excuse to buy more hardware