Actually, US 287 is only the same as I-15 for 40 miles--from downtown Helena, MT to Exit 228. US 287 was once advertised as the "National Parks Route" and the "Gulf to Rockies Route" from Beaumont, Texas to Glacier National Park. It also goes right through Yellowstone NP and near Rocky Mountain NP at the point where US 287 runs from Denver to Fort Collins, Colorado.
For us, US 287 is the shortest route from our house to the south entrance of Yellowstone. It was also the shortest route from Denver to Fort Worth/Arlington, Texas, when my parents lived there. I have no idea how many trips I have made on US 287 since 1957, but it is in the low hundreds.
In fact, I just returned today on US 287 from a camping trip that consisted of a big loop through SE Colorado, the Texas Panhandle, western Oklahoma, and SW Kansas. Midway between Denver and Amarillo, and on the way home last night, we camped at one of our favorite Colorado state campgrounds--John Martin Reservoir SP's Hasty Campground (near the intersection of US 287 and US 50). Weather was unbelievable for this time of year--nearly 90 last week when we got to Amarillo. This morning was a little chilly (36!) so we were glad we had 30A electric and our electric blanket last night.