1) None of your installed versions of ns-allinone can be added to a *PATH,
when you have more than one version.
And : Adding any ns2 *PATH to .bashrc : Not required on Linux.
The binary 'ns' is hard coded to know the location of the libraries.
2) Use a better nam than version 1.15 : The identical 1.14 works better.
The only change that was intended for 1.15 : Can now compile with tcl8.5.
Also : Nam is a separate application. Any nam can be used for any ns2.
A static nam 1.14
Unpack nam-1.14-<arch>.tar.gz, and copy 'nam' to /usr/local/bin/
This nam requires no ns2 libraries: Will even work on an OS with no ns2, no tcl !
All binaries 'ns' can be also be copied to /usr/local/bin/ : One named ns.
And, examples : ns228 (ns228.orig) ns228+<patch-name> ns235, etc.
P.S. : The default build location is /home/<name>/<ns2> :
All ns2 commands should be run as unprivileged user. No 'root'.
'root' is for administrative tasks only.