It should be 15 degrees plus or minus 2 degrees Before Top Dead Center. There is a wide paint mark from 13 to 15 degrees, which the factory probably set yours to. From the 1991 Technical Bulletins, Beginning with April 1991 production, the ignition timing mating mark has been changed as shown below. The trick is to set it to the extreme limit of the specification - 17 degrees. You'll get noticeably better throttle response there.
Advanced timing helps power, but can cause knocking or pinging.
Mine didn't benefit from going beyond 17. I always run 91 octane or better gas too, which lets you push the timing farther without trouble.