Prop Question

[Dogcrew]

I know what you are thinking.....oh no another prop size discussion !!

Not the case here. My SC came with a brand new, spare prop. It clearly states it is 15 1/4 x 15. (Part Number 48-78116 A45.)
All my cross reference research indicates the current size is 15 1/2 x 15.
(new part number QA 2008X)
Is the 1/4" a big deal ?? By the way I have twin 165 Mercs....

Thanks.