I'm thinking of buying a Rode NTG-2, I think this mic is mono. If I plug it into the XLR terminal (ch1) and I leave the 'input channel selection switch' (manual page 44) at 'ch1' will the mic record onto the left (ch1) channel only - and if I position the switch at 'ch1/ch2' will it then record onto both left and right channels in mono ?

Also, is the Rode NTG-2 a suitable mic for use at weddings to pick up vocals from the vows and speeches from around 10 to 15 feet away ?

1. Yes
2. No

Or more helpfully, 10 - 15 feet is pushing it. You would be better to place a mic or mini recorder (like a Zoom H2) much nearer if you can. Some folks use a wireless mic on the groom or officiant for the vows and the same on the best man etc for the speeches. I've used an NTG-2 for similar things but always wished afterwards I'd done it another way.
You would get something, but not that much of an improvement over the camera mic.