Ahhhh soft resetting for a shiny starter takes patience, fifteen hours is a long time but remember some people can go for months before they find one. D:
However just checking up on Bulbapedia, it did say the Trainer ID affected many things along with a secret ID that can be viewed by various methods. The SID does affect if a Pokemon is shiny or not but it didn't say much more other than that, but I don't believe your Trainer ID determines the shinies.If you still need clarifying or want to read more about it, you can go here and check out the info. :3
Hope I helped and good luck! :D.