It is just my personal experience but south of Mochis including Culiacan has never been convenient for me*.Getting something decent to eat at a decent price, hotel rooms, even semi accurate fuel dispensers has always given me a headache. Mazatlan is easier and so is Cd Obregon. And any type of answer has eluded me. They're trying to make Mex 15 all toll road from Noglaes to Guadalajara and it will be a blessing when the work is finished.
*To the point where I have nicknamed the city "Culiacan't"
I have used 57-D as a commute route back and forth from Michoacan and now that the missing element between Queretaro across 15-D to Moelia is finished I doubt I will see much of Mex 15 in the future.
Of course that does not help vacationistas who wish to travel down the west coast visiting Guaymas, Mazatlan and San Blas.
I sort of compare Mex 15 and 57 like traveling down the California coast from SF to Los Angelss. Hwy 101 versus I-5.
From Tucson AZ ro the Junction of Mex 14-D and Mex 200, the interior route for me is a full 3-days faster and seventy dollars cheaper in tolls.
This absolutely does not mean I somehow recommend "Eagle Pass" over "Nogales" but merely makes a statement about travel time and cost. I blast eastward across Arizona, New Mexico and Texas burning a buck fifty per gallon cheaper fuel. Drive until 9 or 10 on interstate highways, use utterly secure rest areas, then head south on a mostly free multi-lane Mexican freeway. The real time eater on the Paific coast is Tepic to Barra de Navidad (Cihuatlan) and then from Tecoman south on Mex 200.
The price paid for the inland route is missing all the attractions of the
Pacific Coast.No beaches no resorts at all. This is a straight logistics money and time question. In fact for folks who have San Cristobal de Las Casas or
guatemala as a goal bypassing the Pacific coast entirely is an excellent idea.
Detour around Mexico, head for Puebla then Villahermosa, to Mex 190 and suffer the 190 topes to San Cristobal. a left turn there takes a person to Guatemala.