The POH of those I used to fly all give a maximum demonstrated crosswind of around 15kt. (I have 3 different PA18-150s in my logbook, and they all had the same 15kt in their respective POHs).
As far as practical limits are concerned, I would say that for a suitably experienced and current pilot, 15kt is fairly sensible for 3-pointers. It's possible to handle much more (well over 20kt) with wheel-landings, but only if you are very current at cross-wind wheel-landings.
8kt does seem very low to me. For contrast, the school from which I rented when I was hour-building several years ago would not have let me fly their PA18s solo had I not been capable of handling 15kt crosswind without having to put too much effort into it.
FFF
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