AX is slow when database is on another server

Hi,

AX 2012 and SQL 2012

When SQL is on the same server as AOS, AX opens fast and everything is done fast but moving it to another server (using the same storage, CPU, ..) it is very slow and sluggish to work with AX. it is opened in about 20 seconds (against about 10 seconds for the first scenario) inserts, forms, .. all slow

The network between servers which are virtualized in ESXi 6 is very good, low latency and ping time is < 1ms but anyway it seems that something is slow there while fetching data from SQL when on another server different from AOS server.

Any help would be appreciated.

Thanks so much