Currently, reference previews only appear after quite some time (300 ms) of hovering. While for #page-previews the delay works well, the much smaller #reference_previews (that often appear right after each other) need a shorter time span. Especially, since reference targets are much smaller than page preview targets, it might make sense to counterbalance this.
See also comment in T214693#4924357
 The delay for the appearance of reference previews is reduced to 150 ms.
 The delay forthe appearance of page previews stays at its current rate
- The delay is about waiting until the popup is being shown. Thus it does not matter whether you have been before.
- This ticket is independent from the bug that sometimes no popup appears if you hover too quickly between preview types
- The code is built in a way that we are never seeing empty popups, in the worst case the popup just takes a bit longer too appear
- The ticket is not about the popup to disappear faster, but about the popup appearing faster