@markbriscoe,
If their notifications are set to send them an email every time there's an update, then yeah, this is excessive.
And it's excessive either way.
Please don't online market this way. It's a waste of your time, for one thing, and it looks like spam to a lot of people. What is likely happening is that, after enough times (whatever someone personally decides; there's no set figure), a person will leave these groups or shut off notifications or they will follow you but block your posts. You don't want any of this to be happening.
Instead, do an analysis of these 60 groups. I bet most of them don't help you that much. Go through them as if you were a customer. Do you scroll on by? Stop? Comment? Want to run screaming for the hills? Your website (you should add the Google Analytics code. If you haven't, do so yesterday) will show traffic sources. You may find Facebook on a whole isn't even a great source for you. You can also alter landing pages to get an idea of who surfs to you from where. E. g. if your painting of a white tiger is only posted on a (I have made this up for the purposes of this discussion; I doubt this page is real) White Tiger Art Page, then if you sell 10 copies and your traffic is coming from Facebook, then you're getting good value - but only for that image and that page.
Learn what is working and do more of that. Learn what isn't working and stop doing that, or change it up that it starts working. I bet you'll find that 5 or so of these groups provide the bulk of your traffic and sales. If that's the case, then jettison the other 55 or just post to them quarterly as a special event and don't otherwise put any time into them.
And start reading
Avinash Kaushik. He's online; just Google him. Read his books or his blog - I have no association with him and get no referral fees or anything for recommending him - but read him! He's forgotten more about website and social media metrics analysis than most people know. Get on the right track with online marketing. This scattershot approach will, ultimately, shoot you in the foot.