Only EP 4 will work with ZC 1.5.x

Good news is that the new EP will not "interfere" with the old EP version. (Which you should just remove from ZC 1.5 - follow the uninstall procedure).

As far as removing the "dross" is concerned, this will need to be done in phpMyAdmin - BUT... you should not go tinkering around in the database unless you know what's going on there. If you do not know how to access phpMyAdmin, it follows that you do not know what it is or how to work with it.

As I said, it IS possible to get rid of this "dross" via phpMyAdmin (I do it occasionally) but it is not doing any real harm, and as there is a risk that your tinkering may actually do some real harm, I recommend you leave it alone for now.