It's depends on how far the two data centers are from one another. But the big cloud providers have data centers in similar locations since they usually want to be near an internet exchange[1]. For example most companies that provide cloud services have a data center in Virginia, USA. So if both data centers are in the same region then you can get numbers in the sub 5ms range. As long as you're not crossing the ocean the latency should be fine.

1. https://en.wikipedia.org/wiki/List_of_Internet_exchange_poin...