In 1.14.4 and lower versions, spruce saplings are not able to grow into a 1*1 spruce tree when there are logs or any other blocks which are not leaf or air blocks within the 5*5 square area above the sapling, but in 1.15 pre1 spruce sapling can grow with logs above them.
For example, in the image below the spruce sapling is not able to grow in 1.14.4 but is able to grow in 1.15-pre1. What we supprose to see: in both versions sapling cannot grow