Been watching the seeming explosion of companies over the past decade or so targeting the mid-grade price-point in the optics market. Cannot blame them, Zeiss Conquest continues with tremendous success, and Cabelas did very well with their past runs of the Euro and Instinct lines made for them by Meopta. To be price competitive or even in some cases undersell the bigger names, some newer companies use a direct marketing approach - Tract is one of them. There are rumors about who makes them, often repeated on blogs and in taverns, but only Tract knows the truth.
I haven’t personally used Tract, but know some aficionados who have and the reports are very positive. IMO Tract, Maven, GPO, MHG, are all very good quality with different +/- in function and design. Just a matter of preferences among this group. The gulf between quality mid-grade and Alpha has diminished but it is certainly still there.
So, do I think a Tract 12x50 will match the optical performance of an SLC 15x56? Even disregarding the difference in magnification, the Tract is a bit overmatched. The 56mm is superior even compared to others within the SLC line. It uses an Abbe-Koenig Prism based optical system, which are superior (in terms of physics) to the standard Schmidt-Pechan Prisms used in other designs. The SLCs are rightly regarded as pretty spectacular with SP prisms, but with AK prisms they are a bit “turbocharged.“ The SLC 15x56 enjoy a sterling reputation for extremely crisp resolution and brightness for a 56mm. The Astro folks love them. The only negatives I’ve ever heard (other than size/weight, which are actually quite good for a 56mm) are glare control compared to the FLs or the somewhat tight FOV - which is mostly because they are 15x.
So, Zack has given some good advice here. Unless money is tight, keep the 15s and buy the Tract. Many times it takes a bit of field time to determine which design is most useful.