10 to 15 HP submersible motors do indeed exist, in either single phase or three phase.

First, there will be the issue of "how deep is the well?" Because this will determine how long your power run from the pump panel at the wellhead will be. If it is a deep well (say, over 200' down to the motor), I'd go with higher voltage (480V vs. 230V) to get lower current demand, which means that your wiring running down the well to the motor might be cheaper. You'll be likely running four-lead wiring down to the pump motor whether you're running single or three phase.

Then you have the question of "single phase or three phase?" Above about 5HP, my preference would be for three phase, but it's your money. There are 230V/1-ph 15HP submersible motors, see the URL below. 

In sizing your generators, there are two ways you could go:

1. Get a generator big enough to do an "on-line" start of the motor. Reckon on at least tripling the size of the generator needed to run the motor at steady state -- eg, for a 15HP motor, get a generator that is in the 35kW range.

2. Get a soft-start motor drive/panel for the motor, so you don't have a big inrush current to get the motor started. The soft-start will bring the motor up to speed slowly. Then you could downsize the generator to be, oh, twice what you need at steady state, say 20 to 25kW.

480/3-ph gensets can also run your house. We have a Multiquip "WhisperWatt" 25kVA genset that I can set to be 230/1-ph, 230/3-ph, or 480/3-ph. Works like a charm for moving pivots or running the house when we have a power outage, is mounted on a trailer with an auxillary fuel tank. When we're running the house, it will run for three days before I have to refuel it.

Multiquip makes gensets in sizes from 12kVA on up to 100's of KW. There are other generator manufactures, of course.
 

Here's a document from Gould's Pumps that answers a lot of your questions in one place:

http://www.goulds.com/pdf/BRCP6SM.pdf