I think the problem with most auto feeders is that they tend to overfeed. This is also combined with the issue that a lot of the food immediately floats down the drain before fish get a chance to realize its feeding time. (The later issue can be addressed with a good controller.) So 15 days of overfeeding, could lead to a nasty water quality problem.

Depending on your fish, you may not need to feed them as often as you think (of course some species of fish need multiple feedings per day). If you have fish that can go longer between feedings, if you have a friend that can feed every 3 days or so, that may be a safer solution.

I personally use a controller to control feedings and have it set to every other day. When a feed cycle is initiated, the return pump turns off for a minute, then the food dumps, then after 4 minutes, the return pump comes back on. This minimizes the uneaten food that floats down the drain which minimizes the chance for a water quality issues. The fish also learn to key off from the return pump shutting off so that they know to start looking for food before the feeder releases it. I realize that this is probably more equipment than the average person has though.