This is a symptom of having too many extensions in your paging ring group. It takes time to setup a lot of individual phone calls. The better solution is to use multi-cast. That approach is unaffected by the number of extensions in the group and is the best practice.
I've not tested this in years, but the last time I did the max number of extensions I could put into a paging group and not have massive delays while I wait for the 'beep" was about 15 phones.... but I assume that delay is, in part, dependent on the hardware running 3CX.
Either reduce the number of extensions in your ring group, or configure the group to use multi-cast. Keep in mind, however, that multi-cast will probably not work if your 3CX is hosted in a separate network (cloud).