Is it safe to take duloxetine (60 mg in the morning) and buspar (buspirone) (15 mg at bedtime) together, or is it likely to cause serotonin syndrome?

Yes: In my experience it is safe & shouldn't be a problem

Ok to take together: I see you are 42. Serotonergic syndrome is very rare anyway, especially in young people. If you develop it, it would be rather unusual event. In Europe, duloxetine is approved in much higher dose. BuSpar (buspirone) officially can be taken up to 60 mg per day. You are not combining very high doses. If your doctor thinks this is what you need, you can take the risk. He has taking this risk with you

It is safe.: However, your doses for both medicines are low. In addition, buspirone, while it is for anxiety, has a tendency to be somewhat stimulating for some people and is often better taken during the day. But perhaps you and your prescriber are working well together and have found that this is not a problem.