They can't be as bad as Lust for Frankenstein. I don't even know if I can finish it. It is so dull, terribly acted and poorly written. I tell my family about the movies I watch, and they'd throttle me if I tell them the worst movie I've ever seen is sex scene after sex scene after sex scene with bad acting and audio that can only be made out half the time. Well, the worst movie I ever experienced, I couldn't finish. That's a story.
I don't know how Tintorera: Killer Shark compares to the Jess Franco movie you're currently watching. It's probably more entertaining and not nearly as inept as the other movies we've listed. Cardona Jr. always struck me more as lazy than inept in his filmmaking. But maybe lazy is more in line with what you're looking for?).
Anyhow, an inept softcore porn did cross my mind. The Jaws porn parody, Gums. Given the part that sticks out the most in my mind, I'd say, make sure you get the uncensored version for the full experience.
In the set of bad movie canon (that getting into some I haven't seen):
There's also a bad movie bible. Which, if this is the movie book, I think there's this one guy who made a host of movies that are described in there that are basically projects in narcissism (he stars in them, and his characters... well, one of them, he's basically a god).
Some other mainstream well known bad movie classics that I've never seen coming to mind: The Apple, Hard Ticket to Hawaii, and R.A.D. fwiw