Bad booster?

Wow I'm running this cam Voodoo Hydraulic Flat Tappet Cam - Chrysler 273-360 268/276 - Lunati Power in a 360 with 9.5 to 1 compression and my brakes work great. I'm no were near 20". I don't think you could get 20" of vacuum unless you were closed throttle going down hill. Most cars have about 19" at idle. Where did he get that number? Your 15" should be plenty with a small booster.