No way is this coin a F-15. The pictures aren't good but it is at least an XF-45 and has some claims to a higher grade. It isn't MS though as it does have some wear.
Basically on type II dollars you don't pay any attention to the details at the center of the reverse because they are often weak or missing just due to the strike.
When they decided the 13 mm type I dollar was just too small they increased the diameter to 15 mm with no increase in weight thus resulting in an even thinner planchet. The the new head design was small and in high relief that resulted in the central portion of the reverse not striking up, there just wasn't enough metal there. Thus the missing letter in DOLLAR and the two center digits of the date. On the type III they increased the size of the head but significantly lowered the relief with the result being much better striking of the reverse.