If you have a 28 day cycle then spotting or bleeding on CD15 could definitely be ovulation spotting. I experienced this a couple cycles and I experienced it with my IUI cycle when I did get pregnant. Good luck. SSBD to you!!!
Don't know enough about your cycles, if you're recently getting off of BCP, if you have any health issues. One theory could be ovulation spotting, another could be that's it's just normal for you if it happens regularly. Best thing to do would be to see your dr if you get really concerned about it.