True. But the idea is that these functions run in between your server/application requesting the object and AWS returning the object to your server. In other words, they happen synchronously with the object request.

So you don't want your server waiting around for 15 minutes on an open request, and most systems won't let you do that anyway (browsers definitely won't). 60 seconds is about as long as you'd want to wait around for your object, and arguably even that is too long. If you need to do some sort of lengthy process to your objects then it should probably be done in some sort of asynchronous queue using a normal Lambda.