Well, assuming it was actually made for 150+mW output powers,
I am assuming that the pump diode inside is perhaps capable opf some 1W output, which would require some 1.2Amps.
Running it at 1.5Amps is a serious overdrive and WILL degrade the diode real fast.
Like I said, it's not made for such powers - people designing that pen never thought to install a diode more powerful than what can be reliable powered by common AAA batteries.
I suggest throttling the current back to ~1A just to be safe. Would be a shame to lose such a nice module!