Red Dead Redemption is not region locked, as detailed in this Rockstar region-compatibility support page.
One of the reasons you may have initially encountered issues purchasing the game the other week, is that there was a server-side issue preventing people from purchasing Red Dead Redemption around the time you posted this question.
As for your inability to redeem the code you bought on Amazon, that may be a different story. The error code you received (
0x80150017) brings up the following description on the Xbox support site:
Error 80150017 occurs when trying to download content on your Xbox 360
You see the following error code and message when you try to download
content on your Xbox 360 console:
"Sorry, something went wrong. This isn't available for your region, or the file is corrupted, or we don't recognize the format. Find more info by looking
up status code 80150017 at www.xbox.com/errorhelp"
This may mean one of the following:
- The content you’re trying to purchase is not available in your region.
- Your billing country or region is different from your physical
Since we know that the content you're attempting to redeem/purchase is available in your region (as it's not region-locked), the error code shouldn't be related to the first potential reason they list. Based on the second reason they list, the error likely means that the region of the Xbox.com site you're redeeming the code on doesn't match that of your console, or that your Xbox account region doesn't match your console's physical location.
If you make sure all of the regions match up, and you're still getting the error, I'm not sure that I (or anyone else on Arqade) will be able to help you further -- you'll need to talk to an official Xbox support representative.