The 15-5 is an interesting revision,
It's .22lr equivelant is the 17-5, both have the wide rib heavy barrel.
Prior to the dash 5 revision the Model 15 was aka the "Combat Masterpiece" available at first in 4" length with a small handful of 5" guns on special runs, a 2" snub came later but it had a different frame and barrel than the 4" and 5"guns, if you go back to 1946-47 SW offered their new post war 6" target trio in .22lr, .32 and .38 Special, these new ost war guns all had a narrow raised rib on their barrels.
Around 1948(ish) SW tested a 4" version in small runs, in the 1950 All model circular (AMC) the 4" became a regular model offered to the public, Interestingly the 1950 AMC also introduces the new wide rib "K38 Heavy Masterpiece".
This was done in an effort to weight match the three 6" target Masterpiece revolvers since the smaller the bore the heavier the gun, this was accomplished in the barrel and rib thickness.
By 1954 the old narrow rib barrel ceased production and all three 6" Masterpiece had the wider rib barrels.
Strangely the 4" "Combat Masterpiece" continued on with the old narrow rib barrel profile.
This continued up until the dash 5.
For some reason the 15-5 suddenly got the wide rib barrel from the previous Model 14 line and was suddenly offered in both 4" and 6" lengths( might be an 8,3/8" option too).
About the same time the Model 14-5 gets a new full underlug barrel in both 4" and 6" ( maybe 8, 3/8" too).
At the same time the .22lr counterpart Model 18 line is discontinued and the Model 17-5 is offered in 4" and 6".
The 4" Model 15-5 doesn't pop up too often but the 6" version almost never pops up.
