There's no simple notion of how much memory is used by a program.
The output of
pmap describes all the virtual memory that's mapped by a process. Mapped means that the process can access that data through a pointer, without issuing any further command to load data or request access. Mapped virtual memory isn't always in RAM: it can be swapped out, and it can be in a file. For example, all the shared libraries that are used by a program are mapped in each process that uses them, but (for the most part) only one copy is kept in RAM for the whole system, and that copy need not be fully loaded in memory (parts that are required will be loaded from the disk file on when needed). The 1.5GB figure includes all of the process's code, static data, shared memory and own data. It's not a very meaningful figure.
pmap is a simple reformatting of
/proc/$pid/maps. Understanding Linux /proc/id/maps explains what the columns mean.
The 450MB figure is (I think) the process's resident set, that is, the non-shared memory that is currently in RAM. This includes both data that belongs only to the process (and which may get swapped out), and files that the process has opened for writing (disk buffers, which may be evicted to be reloaded later from the file).
You won't easily be able to break down the 450MB memory further. This is a job for the program's author, with debugging tools.