That's about right wd. 15 oz. brings it to about an inch to inch and a half below the top with the springs in and top tubes collapsed.
We've had several occasions where someone had no oil at all and didn't realize it... so less won't hurt you.
Filling to the top will increase air pressure when bottoming out and increase the risk of blowing out the seals. So don't do any wheelies... wd!
But for us normal folk, guesstimating the spacers are about 10" long, adding an inch of oil will only increase the pressure 10%. That should be acceptable.