My son lives in SLC, and we visit at least twice a year. If you hit the 15 during non rush hour times, it's actually no better or worse than any other large city. It sounds like you just had an unfortunate incident.
The one thing that drives me crazy about the 15 though is it always seems to be under construction. I'm hoping when we go up there next month that most of the construction is done.
2016 Ford F350 Turbo Diesel SRW 4x4
2017 Grand Design Reflection 297RSTS
2013 Ford F350 Turbo Diesel SRW 4x4 (Destroyed by fire - 8/29/16)
2014 Grand Design Reflection 337RLS (Destroyed by fire - 8/29/16)