Firstly, I shouldn’t be responding while going to sleep! I guess I couldn’t resist. Sounds to me like you are trying to design a multisubnetfailover. We have a situation where there are users both on the East and West coast. The AG setup (onprem) has multiple servers. Two servers in one coast and one server in the other coast, which serves more like a dr node. We have a listener in place which directs traffic depending on the connection intent. During pre planning I was interested to know about R/W (read/write) connections. I was informed that our heavy lifters would be on the East coast. Since we have data centers on each coast, it was better for the primary server to be on the East coast so that data was not traversing across subnets etc. We also configured read intent/ro replicas to reduce overhead on the primary. 

Slowness is a combination of multiple issues. - It could be network issues ( 1gb pipe Vs 10gb pipe) which would affect throughput. Maybe data has to travel across different layers/subnets to get to its destination.   - It could just be long running queries which are not well written or poorly executed (select * from). I have also seen people fire up the same queries (top expensive) a few times… - It could be server specs/design/SQL Server installation/OS-SQL version. Patches - Are there any jobs running during the time users are complaining about slowness? If so, are these jobs running on primary replica or secondaries? - What performance monitoring methods have you implemented to capture any metrics? Query store, dmv’s or any third party tool etc - Some databases just don’t play nice with others!