I've written a few posts lately about ways to speed up Lightroom, and there's one more that may seem counterintuitive at first. If you have a lot of develop module presets installed, it can slow down Lightroom. It doesn't just slow down Lightroom in the Develop Module either, it slows it down the whole application. Even if you're just in the Library. I had written about this before, and I had thought that this "bug" was fixed ages ago. On an official forum, an Adobe rep said that this was to be fixed in Lightroom 6, but it still seems to be an issue.