You found the right forum.

I would suggest that if you're going to be locking bike outside to spend a little less on the bike, preferably a used one that doesn't appear to be worth stealing. Invest in a good lock. It feels great to ride a fancy new bike, but imagine how you'd feel if you came back to it after work one day and it was gone.

If you ever have the option of storing it inside, then that's a different story.

I can't suggest a particular brand or model of bike, but make sure whatever bike you buy fits you well, because if you're just starting out 15 miles is a considerable distance and you'd conceivably be spending over an hour on it each way.

There are different option for storage. I have a rear rack and pannier bags, which is probably the most popular option. But you could always just make do with a backpack, or a messenger bag, if you don't like to have a warm back.