15 minutes is a bit long, but not out of this world. As the Apple article says, when safe-booting the system verifies the start volume and does a file-system check, and repairs as necessary. This can take some time.
I would try it again and wait something like 40 to 60 minutes before interrupting the boot.
If this fails too, then there is probably some non-trivial issue with your system or start volume, which might require a reinstall or a re-partitioning.
PS:
You really should do it when you have time. It’s not something you do while preparing coffee. Not only because of the longer boot time, but also because once in safe mode it usually takes some time to definitely tell if the issue has gone away or not:
Unless it happens that you can reproduce your memory issue on the first attempt, you’ll have to try different scenarios to reproduce it. Only then you can really say, it has gone away.