The Conversion Unit not introduced until 1938. (The term "Conversion Kit" was used only occasionally during the later years of production, with no particular pattern as to when the "Kit" term was used, and when the "Unit" term was used. Someday, I will have to do a catalog analysis to determine when each term was used.)
As stated, there is therefore no "era correct" Conversion for a 1915 Government Model. The "most correct" would be a "U" serial-numbered Conversion from the 1930s. Expect to spend well into four figures for a nice example - if you can find one. (I have a reblued, unboxed, serial-numbered Unit (U1XX - shipped August 23, 1938) with a factory letter for which I would take $925 delivered if that would interest you.)
All genuine Colt Conversions are functionally the same, except for the Series 80 and Ace II units. The latter two will not work "out-of-the-box" on a Non-Series 80 pistol. The firing pin safety mechanism would have to be removed to make them work.