Just to clarify, 15 speed for missiles is not fast at all. We're not reverting the fungal nerfs. And the 10 range is nowhere near as good as the instant fungal at 9 range. There's obviously a higher chance to miss with this current fungal if you shoot it from a longer distance.
We really liked playing with this version of Fungal Growth internally because the tradeoff between getting in closer for more accurate fungals vs. shooting from a safer distance for less accurate fungals is working out decently well.
However, we can only test so much internally is why we'd like to try the change in the beta. This, just like everything else in the HotS beta, is not final.