I have both a 915 and a 910 pistol. Both early production examples.
First, the 915 and 910 are similar in appearance, but are NOT "the same". The only thing that is the "same" about these two models is the mags they use, and the S&W logo stamped on the slide.
The 915 does NOT have plastic parts. The 915 has metal sights, metal guide rod, metal mag release, and metal disconnector. The 915 also has a lug on the barrel and a corresponding cut in the slide for tighter lock up. The 915's tighter lock up can be seen in its increased inherent accuracy over the 910 pistol. My 915 is a tack driver.
The 910 has plastic sights, plastic guide rod, plastic mag release, and plastic disconnector. The 910 has no lug on the barrel, nor a slide cut.
The 915 has better fit and finish than the 910 as well. The 915 will fit 5906/5904 leather. The 915 has a nicely contoured slide and frame.
The 910's block like slide will not fit in 59XX series leather. It will fit some Glock holsters.
My 915's previous owner was the Chief instructor at the S&W Academy. He had the Performance Center do a trigger job on it, and cut the slide for Novak Low Mount night sights. Personally I think this not only improves the utility of the pistol but the looks as well.
Nice 915's can be had for $250 to $325. Much less than the asking prices for 910's, making them a superior value as well as a superior handgun. I personally prefer the 915 to any M&P pistol as well. Much better trigger, and is 100% reliable.
I'd go $375 for a LNIB 915 with box & docs, plus two mags, before I'd go that much on a 910. Good luck! Hope this helps. Regards 18DAI.