it was public about 1 year ago, but it was or is a pain in the ass to update it to newer patches, i think right after kabam changed big parts in the internals of the game that made it so hard to update.
ask nilly, she's the author of fsv3.
if u want to, you can try changing the "16" in the fsv2_3.txt file in the fsv2 mod to something lower, and see if that reduced your lag: this reduces the distance you can see enemies(?) pop up. it is normally set to "1"!!
i do not remember what exactly made fsv3 less laggy, maybe someone else (Nilly?) can tell us :P