Summary: install the LedgerSMB web proxy package 'ledgersmb-1.5-apache from the LedgerSMB PPA, which will install the main 'ledgersmb-1.5' application package & do some basic setup for the web proxy. (In your case, of course, it will not need to also install apache itself since it's already installed for the old LedgersSMB version.)
Thing is, due to the current lack of some dependencies, a version of the LedgerSMB 1.6.x series has not yet been backported to Ubuntu 16.04 (xenial), not even our alternate package 'ledgersmb-1.6'. Our alternate package ledgersmb-1.5 is available, with the most recent one being for LedgerSMB version 1.5.24 (which is the most recent release of the LedgerSMB 1.5.x series).
Note that our alternative packages (and some of their dependencies, depending on the Ubuntu version) are available at:
https://launchpad.net/~ledgersmb/+archive/ubuntu/main
If you all are not yet familiar with the more recent versions of LedgerSMB, how they are run has changed in that the LedgerSMB application is no longer run directly from Apache like is the case with the LedgerSMB v1.3.x series. Instead it is run locally on the server being used by 'Starman' and can be made available from that server by a web proxy (via SSL by default). The ledgersmb and the ledgersmb-1.x packages do this slighty differently, with ledgersmb-1.x explicitly having additional packages for the 4 main web proxies that we support directly (with example configuration files); apache, nginx, lighttpd & varnish
Any questions, comments, etc; please let us know.
Robert James Clay
jame@rocasa.us, rjclay@gmailcom