The memory model is completely different now and you should not compare the numbers directly. The new model is managed by Windows (similar to Windows Store apps): as long as you have enough free memory, Windows allocates as much as possible to apps like Listary to speed up future operations. Windows may also gradually recycle memory if you keep apps idle for some time (like 15 minutes). If your previous memory usage is 15M, it could be 50M now, which really isn’t much, just one Chrome tab.
Can you upload one screenshot of your index setting and one of Listary’s search results?