Part of the problem is that the PCs that partake in the 15-minute workday still make good XP from doing so. Take that away. No XP for monster kills. No XP for traps beaten. No XP for quest objectives. Award XP if, and only if, the PCs recover treasure and return to town with it; determine the GP value of the recovered treasure, and award that in XP to the surviving PCs as a group reward that must be evenly split.
Those goblins? 0 XP. The pit trap? 0 XP. Getting the princess back? 0 XP. Hauling the goblin king's treasure chest back to town? XP awarded.
The result? The PCs now has an incentive to (a) avoid useless encounters and (b) keep moving on instead of wasting resources on things that don't matter.
I've been working on a system where you get XP based on the number of "successes" it takes to overcome an obstacle.
Kill an enemy in with one spell, you get a handful of XP. Teleport from city to city and evade all those encounters and get little to no XP. Engage in an epic struggle that takes lot of attack rolls, healing and whatnot and you'll get tons of XP. Devise and execute a plan where you bribe, bluff, extort or sneak past the king's legion and you'll get a whole lot more.
The hard road becomes more rewarding, the easy road less so.