Nav NST Consume all memory

We are facing a problem of Nav service exe memory usage goes high and server gets hang.

One reason we found that the users which are connecting using 1mbps line (wireless) consuming lot of memory for NAV service(WAN). So we asked client to user a terminal server which connected to NST and database in LAN environment.

But still we found that in LAN also sometimes Service Memory goes high. For example copy the data put it on excel do the changes and again putting back in nav.

Another finding is Sql database is not segregated on different drive (Ldf/Mdf/Ndf). TemDb also not move to different drive.

Does the Navision NST exe get affected because of the above Sql issue or is there any other issue?