I've submitted this as an SMR through TS, but I figured I'd get others' input as well. We do have a series of clients on 15.2.x running WCM/RiSE and almost all of them have complained about page load times. Some more loudly than others.
A particular site is continually taking 8-16 seconds to load pages (while they claim it takes upwards of 30 seconds to log in). Another client is taking up to 12 seconds to load pages - other sites running WCM/RiSE are taking 5 seconds to load a page. screenshots from 3 different clients: