In a sense shortening the life span for Sims next year would make things more difficult mainly because you'd have less room for error - there would not be much time for you to recover from mistakes. But, whatever goals the team sets up for an event - making money, having lots of kids and moving them out, capping as many careers as you can - life span really does not play into difficulty. You simply would not be able to make as much money, move out as many kids, put together as many collections, etc because you'd have less time. But, chances are - you'd do exactly the same strategy on Short as you would Normal. You're always going to try and hit it out the park right out the gate no matter how much time you have.