Will try to keep this simple:
2008 server running SQL Express 2008 with front end access 2010 or 2013 runtime client using a pretty small, simple database, on W7 PCs
Server replaced with 2012 server, much better spec, more RAM etc. and 2014 Express. Database ported over. Nothing else changed - network, PCs and front ends identical. 2012 server connected to network on same cable as previous one.
Database access is now much slower on all PCs.
I have played around with network settings a little on the clients and next step is to update network drivers on the server, but any other pointers gratefully received.