Have no idea what 12/15 half wave amp means. Did try a 15A and it blew right away.Usually these regulators are the 12/15 half wave amp version. So I would fuse at @15 amp.
And yes most DIYers usually go a little over board but that is normal. Just shows lack of experience. Heck many shops do the same thing as they also lack electrical experience and knowledge. But I do have now have 45 yrs of experience doing it so I am little more into the testing stages.