I get the point that you are making, but if something really only takes 15 minutes to do, I wouldn't necessarily use an open source solution just because one exists.
Depending on the situation, the library may have a ton of extra bloat that your application will never use. Also, recklessly deferring to open source libraries can potentially snowball into something like the left-pad fiasco[1].
Yeah, and I get your point too. Eight lines of code? Yeah, you don't need a library. But usually when someone says "15 minutes" they mean 1 - 2 days. So things of that complexity is when it's obviously you should choose a good OSS lib.
Depending on the situation, the library may have a ton of extra bloat that your application will never use. Also, recklessly deferring to open source libraries can potentially snowball into something like the left-pad fiasco[1].
[1]: http://blog.npmjs.org/post/141577284765/kik-left-pad-and-npm