For what it's worth, maximizing HS triggers across a party is optimizing the party for single (or linked, no short rest) massive encounters. The problem the OP is having is that he cannot challenge the party without draining the party's daily allotment of resources (because the party can drain their full allotment of HSs in a single encounter, or at least one character's HSs).
This has nothing to do with players choosing to take 15 minute adventures, but rather with the DM feeling that he has the choice of not challenging the party, or forcing the party into 15 minute adventures by facing them against brutally hard encounters. Providing the party with incentives to push onwards/penalties for not pushing onwards is irrelevant to the problem at hand.
I would say that, given the party's build, design an adventure fairly normally, cut the opposition a little (the party will be using fewer Encounter abilities, although it may be able to get more juice out of some Dailies) and link the encounters (so there is no time to short-rest) into a few mega-encounters. This generally has the side benefit of making locations feel slightly more reactive to the PCs' presence. Don't force yourself to strain the PCs' resources in each encounter, by try and make them burn a daily HS trigger or two each linked-encounter: they'll notice that.
I *strongly* recommend having the "second" half of a linked encounter arrive AFTER the first half is completely over until you get a good, solid grip on the balance issues. In the absence of strong AoE abilities, encounter difficulty tends to go as the square of the number of opponents, which can get out of hand really fast.
This has nothing to do with players choosing to take 15 minute adventures, but rather with the DM feeling that he has the choice of not challenging the party, or forcing the party into 15 minute adventures by facing them against brutally hard encounters. Providing the party with incentives to push onwards/penalties for not pushing onwards is irrelevant to the problem at hand.
I would say that, given the party's build, design an adventure fairly normally, cut the opposition a little (the party will be using fewer Encounter abilities, although it may be able to get more juice out of some Dailies) and link the encounters (so there is no time to short-rest) into a few mega-encounters. This generally has the side benefit of making locations feel slightly more reactive to the PCs' presence. Don't force yourself to strain the PCs' resources in each encounter, by try and make them burn a daily HS trigger or two each linked-encounter: they'll notice that.
I *strongly* recommend having the "second" half of a linked encounter arrive AFTER the first half is completely over until you get a good, solid grip on the balance issues. In the absence of strong AoE abilities, encounter difficulty tends to go as the square of the number of opponents, which can get out of hand really fast.