[Also,is it a boxlock,or what?]
That's a little like saying: "I have a gun - can anyone tell me what it is, when it was made, etc ?"
It's just waaaaay too little information.
Pics are best, along with physical specifics, like - does it have external hammers ? Does the action have side lock plates ? Are there any markings on the barrel undersides, between the hinge & forearm stud ? Are there any markings inside the action ? What GAUGE is it ?
Generally, although not always, if the rear of the action metal is squared-off, where it meets the buttstock ears - it's usually a boxlock action. Floorplate actions look the same from the outside, but Stevens didn't make any of those.
Sidelock shotguns have side plates for the locks - ala L.C. Smith's & higher-grade European shotguns.
AFAIK, L.C.Smith was the only US sidelock maker - which should make your Stevens a boxlock.
1915 is when Stevens advertized that they are now making their own shotgun barrels, with the lug integrally forged - instead of buying barrels from Belgium, as did most others - since World War I was looming, and the barrel supply was disappearing as countries fell to aggression.
At that time, Stevens was one of the largest, if not the largest firearms manufacturer in the world- so they were able to do things that other companies couldn't/wouldn't.
Stevens would have marked the barrels with that statement for a very long time - but I don't know if/when they stopped marking them such.