No, nobody's hacking you, this is a browser in one of your devices trying to render a tab left open or generate a thumbnail for a URL from its most visited / top sites.
Yes, your laptop is hibernating but it may be waking up to do small amounts of work such as fetching emails. Apple calls it Power Nap, Intel calls it something really long and complicated but they work the same way. Or you may additionally have a smartphone, tablet, or smart TV.
The fact that these access attempts happen once every 15 minutes (give or take a minute or two) seems to point towards the power nap family of features.
Solution: close all browser tabs to your site's administrator when you are done working with them AND make sure your site's admin pages are NOT included in your browser's frequently visited / top sites.
PS: Yes, it's happened to me too, a long time ago. That's how I know about it.
Nicholas K. Dionysopoulos
Lead Developer and Director
🇬🇷Greek: native 🇬🇧English: excellent 🇫🇷French: basic • 🕐 My time zone is Europe / Athens
Please keep in mind my timezone and cultural differences when reading my replies. Thank you!