If my memory serves me right, some did have similar queries about the Kapex and CT26, CT 36 etc., and I do not recall anyone ever toasting their CT dust extractors using the Kapex. As far as I know. all Festool showrooms hook up their Kapex to a CT26, etc.
Frankly, if I couldn't use the CT15 with my DF500, I wouldn't have bought it.
Technical Data for CT 15 E HEPA Dust Extractor
Power consumption: 350 W-1,200 W
Max. appliance socket connected load: 2200 W