You only drive 1500 miles per year. As long as you use a quality
oil, it's not going to be "bad" after 1500 miles. I wouldn't hesitate to leave it until spring, and then put fresh
oil in it for the new season.
If you're not sure, send a sample to Blackstone for analysis. I'll bet the pH hasn't changed any from new. For $12 you get the definitive asnwer, not some ones opinion.