I've heard they last about two weeks. Is this true? I've never used them before, so I thought I'd ask you.

It depends on where you get them from, if you choose a good brand and use the lamp correctly, then they can last up over 14 days. You can see more about doing the proper way here: How to apply semi-cured gel nails.

With quality preparation of nail plates, strict adherence to the rules of gluing sliders manicure will last at least 2-3 weeks. But the wearing time largely depends on what materials are used.
If the film begins to fall off quickly, it is likely that it was glued to not fully dried coating. It is possible that the sticker itself was very wet.