I find it quite strange that yours has grown so slowly, according to this (
http://onlinelibrary.wiley.com/doi/10.1111/fme.12082/full) at age 1.5 the mean length of P. pinirampu was nearly 16", which aligns with Amiidae's comments in the Planet Cat thread. You clearly take excellent care of your fish so I'd rule out stunting, though I suppose it could just be a slower growing specimen, wild growth rates are not an absolute. A very, very interesting fish indeed.