I'd be sure to outfit it with tires that can take 100psi of pressure vs 85psi which is what the stockers on my giant were
High pressure does not equal 'great tire'. Wider width tires tend to have a max PSI lower than narrow racing tires. For example, my Conti Contacts have a max of 85psi (but are 36mm wide) and are made for traveling many miles over rough pavement.
Jake, I would look at bikes with wider road tires (30mm+). These will not affect your top speed an will be much more comfortable on rough pavement. Narrow tires are lighter and are worth it for acceleration and climbing (you don't care about either). Regarding 'drops', know that you can ride along with your hands on the tops (crossbar or the hoods) and that should be comfortable depending on the bar height.
With a 15mi commute, you will likely need/want more goodies than someone who is doing a 1-2mi commute. Some things you'll want immediately, others you can get as needs dictate. I started out doing 9-10mi each way until I moved; now I have a 1.3mi commute. Below is what I used (before and after):
- Higher end lighting system (busier roads, I like having something bright & noticeable)
- Quality saddle (most saddles that come with <$1k bikes are junk)
- clipless pedals & shoes (once your cadence gets up you will find that these are a plus)
- bike clothing or dryfit clothing (bike shorts, wicking shirt and socks)
- Extra water bottle (during hot summer days)
- Rack and pannier (sweat soaks through a backpack)
- Change of clothes & shower gear at work
- spare tube & tools to repair bike
- bike lock (kept at work)
- Full size pump (top off my tires each morning)
- travel pump (carry in bag in case of flats)
- some form of flasher and front light for night visibility
- backpack to carry laptop, spare tube, & tire levers
- travel pump (pump and tube could be ditched if you don't mind walking or had a cell phone for a ride)
- full size pump (top off tires at home)
The first list is at least a couple hundred bucks, the 2nd list is ~$100 (for stuff that works).