Yeah, your scenario is a little different. You paid an appropriate price for an OK frame/project bike ($15).
(With the same money, one could buy an old steel frame set that weighs about the same as the heavy Al Schwinn) You're capable of fixing/modifying the bike, so again you're several steps ahead of the OP.

I volunteer at my local bike co-op, where we spend an hour or two on each donated junker to attempt to get it safe and ride-able. Most are barely-used dept-store bikes, but they're already broken or worn out, or just never worked properly from the store. Some of these still end up broken down and scrapped because they're not worth our time to repair; like lipstick on a pig.

I agree with the majority that dept-store bikes deserve their moniker as "Bike Shaped Objects (BSO)". They're a poor investment new, because of indifferent design and specifications, and often incompetent initial assembly and tuning.

You can spend ~$300 at your local bike shop and get a bike that has only slightly better components than the Wal-mart Schwinn, but is expertly assembled and tuned, and will have the bike shop's guarantee behind it.