I would not drill the groundwork. I don't find it that interesting and neither do many horses. If you are finding that you are working at this stuff 15 minutes per day, nearly every day that you work with this horse, and you still feel as though the horse isn't where you would like him to be with his ground manners, you should perhaps reconsider how you're training the behaviours you want, or don't want.
I virtually never do groundwork with my horse, because I've done it and instilled the behaviours I want, and there is no point in continuing to drill the horse on behaviours she already knows. If anything needs reinforcing or reminding, that happens in the normal course of catching/grooming/tacking up. If the horse, for instance, tries to push ahead of me while being lead (my BOs let her do this when they bring her in, so occasionally I have to reminder that it's still not cool with me), I stop and back her up a couple steps and she says, "Oh, sorry about that, right." That correction will have taken about 15 seconds and because the horse is trained, she knows exactly what the correction is for and I don't have to "work" with her on anything. As I look at it, once you've trained ground manners, you should not have to devote any substantial time each day to ground manners.
To get to this stage, you have to be sure that your completely clear in how you reinforce behaviours and what behaviours you are reinforcing. I would recommend reading everything Mark Rashid has ever written, as I think he is exceptionally succinct and precise in terms of how he explains how "bad" ground manners are learned behaviours, same as "good" ground manners, and it is up to the trainer or handler which ones are positively reinforced.
I too want to show up at the barn and just ride, but I want the horse to be easily handled from the moment I catch it to the moment I get on its back. So I will do the groundwork until the horse gets to that stage, but once it's there, it's there.