Effect in Latency if APAC O365 tenants will be accessed in Europe

It depends, because a number of factors come into play.

First, the speed and quality of the local network.

Second, the capacity of the connection to the internet.

Third, the closeness of the nearest Microsoft connection. Microsoft has a large number of network endpoints deployed around the world to bring traffic into their global network. Once the traffic enters Microsoft's network, it's transmitted across fibre connections and it really doesn't matter how far you are away from the target datacenter.

 

By far, the biggest issues and bottlenecks come from local networks and internet connections (the last mile). My tenant is in EMEA and I connect to it quite happily from all around the world.

To address this question I recommend you to use the resources you can find in the following support article: https://support.office.com/en-us/article/network-planning-and-performance-tuning-for-office-365-e5f1228c-da3c-4654-bf16-d163daee8848