It's just fine. Often with a good size bowl full I'll get called away or distracted after ten or fifteen minutes, and leave it partially smoked. It's sometimes even better when I return a half hour, two hours, a day even, later.
I'd suggest smoking your pipe however you wish. If you do not like a short bowl, don't do it. If you prefer long, contemplative bowls, do that. I've always considered the pipe to be something I enjoy on my own terms. I'm not here for the pipe! The pipe is here for me.
Sure, if 15 minutes is what you have, and you'd like a smoke. Like the above post says, you can smoke in installments, over a day or two, no big deal. Sure, I prefer a leisurely smoke, but sometimes a short puff is pleasing.
Of course, 15 minutes is better than nothing at all, yet as the undersigned, its that for why I do have smaller bowl pipes and even with these I don't always fill them up but only half,naturally when am going this way I feel they tend to smoke hotter&wetter
If I only had 15 minutes I would opt to not smoke. 45 minutes is about the minimum for me. I've been cut short before, only getting about 30 minutes in and just hitting the sweet spot before getting interrupted. I felt cheated and grumpy!