Yes absolutley, the same applies to user passwords - basically everything. If you only have one DC and restore it from a 15 day old backup , then everything is reset back to that point. Any computer or user passwords changed since then will be invalid.
The error message you described is due to computer account passwords being incorrect but the same applies to user passwords so any changed in the last 15 days will need to be reset, or if they can remember their old password, use that to login.