Generally the preview packages are a good deal. All depends where you want to go and if you're interested in staying there. I'm not sure which property you're talking about here however.

The 199 covers your room. You'd have to check the fine print if there are taxes on top of that, but usually it covers the stay at the resort. Any incidental spend for food/beverage etc is your responsibility to cover.
For points vs resort credit, I'd take the $75 over the 15k points since you said you don't stay at Marriott hotels. The points wouldn't be of any benefit to you.