Welcome to the forums Kevin, you have a great looking place!
The most common pump for this application will be the traditional sump pumps that you find in basement sumps or septic lift systems. But, when you find one that can handle 15 foot of head, the GPM is typically much more than you need. This application would require float switches to handle the differences between the variable well flow and the output of the pump. It is practicality impossible to match the well flow to the pump flow without adding substantial cost to the control system.
My advice would be to make the sump (or cistern) as large as economically possible and place the sump pump at the bottom with a 'ON" float switch as close to the top as possible and the "OFF" float switch just above the pump.
Imagine a five gallon bucket as your cistern with a pump that puts out 10 to 20 GPM.., the pump would be cycling on and of every few minutes. This uses more electric than cycling less frequently. Now, imagine a 100 gallon cistern with the same pump. At 2 GPM well flow, your pump would only kick on every 50 minutes and have the cistern empty in just a few minutes.
I would suggest contacting a local septic service company for the right pump and float switch configurations. If you decide to go with a smaller pump than they have available, they should still be able to help with the float switches.
Here is an example of the type of pump I am thinking off....
McMaster Carr # 4182K5
https://www.mcmaster.com/4182k5This supply company tends to cater to companies that need it tomorrow and tend to be on the high cost side, but their site is a great reference for things like this.
