FWIW, there was a bug in darktable 3.0 that caused massive slowdowns with large libraries. It was fixed shortly after release and is in 3.0.1 (and the master branch, of course). This affected not just the lighttable view, but also the darkroom too. Edits were much slower.
If you have a large photo collection in darktable, be sure to upgrade to 3.0.1. Between this one and a ton of performance improvements, you might be able to postpone a laptop upgrade a bit longer. 