I'd be very apprehensive about a 915 with a "nickel/stainless" appearance, especially if we're talking just online pictures.
The 915 is the only 'value' gun 100% compatible with the 59xx series, meaning interchangeable barrels etc. The 910 etc, have different barrels.
This means a lot when it comes to working on and replacing parts. You want to stick close to the 59xx guns, because there's a lot more stuff out there.
S&W never made a nickel, stainless, or otherwise "in the white" 915 to my knowledge. So, absolute best case scenario would be an aftermarket finish. Kinda unlikely for a bargain gun, when you could get a 5906 or 5903 instead (5906 is stainless slide and frame, 5903 is alloy frame to match stainless slide). 915 was carbon steel blued slide, black anodized aluminum alloy frame.
If the frame is shiny but definitely 915, it's very likely had the black (and anodized) finish sanded off or beadblasted, and thus would be soft.
2nd best case would be 2-tone, black frame, stainless slide from a 590x gun.
You can get a 5906 for about $300 and know what you're getting. I wouldn't gamble on a 915 that looks "different", odds are that gun has had a very rough life and not worth much at all.