advanced timing, anybody else doing it? Options

[6strngs]

so, after having read about how advancing the timing a couple of degrees on this car can make a difference, I decided to advance mine. took only a couple minutes and my timing was set at 15 degrees BTDC. my idle now sits at about 900-950 as opposed to about 750 like it's supposed to be. but when I started driving I felt the difference right away! it's not uber dramatic but it's noticable. especially in the low rpms, from like 1-4K, and it feels like the normal power drop at 5500 isn't as sharp, I mean, it's still there it just doesn't feel like it drops as sharply. I'm running 91 octane gas with and I didn't feel/hear any detonation, even when I tried to put the car under load by riding it 4th at 1400 RPMs I didn't notice any. I'm thinking of either going back out and setting it to 16-17 or just using 89 octane. anybody else done this?