I also bought a S&W 15-6 recently in 38 special 6" barrel.
Serial # BJB7231 purchased in Canada.
I am the 3rd owner. Was BNIB to second owner.
I also have the original box.
I think it is early 1990's but would appreciate any info you can provide.
Pics attached.
After the model 14 was (temporarily) discontinued, the model 15 was offered with 4 and 6" heavy barrels; the latter (the one pictured) is a model 14 in all but name. Enjoy!