Glad to report some good news. We've a previously used a Geotrust Truebusiness ID Wildcard certificate to secure our RemoteApp servers and after a bit of head scratching have now used the standard FMS 15 admin console to use the same certificate to secure our first v15 server.
No need to use the command line (for the first time), we did have to create a new certificate signing request file and get our wildcard certificate reissued based on this (no cost, just a web page to put the revised CSR in and a new certificate/intermediate certificate issued by email - a minute or two). Nice green lock icon on the FMP v14 and v15 clients.
So it looks finally as if we don't have to continually purchase individual certificates for each server or combination of servers for 2-machine deployment and can finally see some cost saving for a software update.
We're now looking forward to doing some back to back speed tests in comparison with v14 server.
+1 for FMS v15