How can my neighbour and I share his broadband?

My neighbour is getting a high end broadband service installed, and we are looking at sharing the costs as it's quite expensive but over 15x faster than standard ADSL broadband in our area, which is not served by cable. I was thinking of getting a 12dBi transmitting antenna to put on his back wall (next door but one to me) facing into my back garden, and connecting it to his router. Then getting a 10dBi receiving antenna mounted in my garden and connecting it to a booster/repeater in my house. The distance is about 15m-20m away, will this work and keep the 15mb connection in tact? Otherwise, what alternatives are there to transmitting a WiFi signal across a distance like that, and are there any options whereby we wouldn't need antennas?