Large Files

This is normal. The game's program files, as in, whatever you install through Origin or disc or Steam, are always a certain size and don't change, and you shouldn't modify them either unless you have a specific goal in mind and know exactly what you're doing. The files in Documents > Electronic Arts > The Sims 3 are the ones that grow and change as you play and add content.

How long a save takes to load depends on your computer's hardware as well as the age and complexity of the save. My current save, 75 weeks in and rotational (I've played most of the households so far), loads in about a minute (from the Main Menu to live play), which is twice what it took when new. I also have hardware that's overpowered for Sims 3, so it's not necessarily a useful comparison.