Just my opinion, but I think it would be better to leave the right main where it is rather than move it. You'd end up with all the audio coming from the left of the TV which would be weird.
The problem with the mains being 16 feet apart, and you only 8 feet away from them, is that it may leave a hole in the center. Normally the center channel speaker can be used to fill in any such hole, but you've got a problem there as well. If you center the center channel speaker between the two mains, it will be to the left of the TV and dialog will sound like its coming from the left instead of from the TV. If you place the center on/below/or in front of the TV to get the dialog in the right place, you're back to potentially having a hole in the middle. However, adjusting the volume levels of the respective speakers, and properly setting their distances, in your receiver can help all of this. You'll just have to experiment.
I'll pass along Ray3's normal advice in a situation like this. "Sell the wife" and place things where they ought to go. (Please don't tell her I said that. Hell hath no fury......ya know! Actually I didn't say it. Ray3 did!
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