Heck, isn’t there a section of I-15 near there where the posted speed limit is 80?
Yes. Multiple sections. North bound I-15 starts the first 80 MPH at Enoch,UT around MP80. It drops back to 75 MPH near MP100 so you can negotiate the Beaver area passes north/south. 80 MPH occurs another 3 segments that run 15 to 20 miles each. I just traversed that path last Friday. There are no 80 MPH segments on I-15 north of about MP210.