About a year ago i installed 16gigs of RAM in my iMac specifically to aid performance with Aperture. Since upgrading to El Capitan, things have really slowed down - I'm waiting upwards of ten seconds to load 24mps images which used to just snap in with absolutely no lag whatsoever. Ten seconds doesn't sound much but with 200+ images to sort and edit, its a real bummer and takes the gloss off my photography. I would happily tear a new one on the guy (or gal) at Apple who decided to dump Aperture.
My strategy, having been very pleased with Affinity Photo and Designer, is to stick with a very slow Aperture and wait for the Affinity product but I've got to admit it cannot come soon enough!