How to measure an 15 kV electric fence to 0-5 v analog input of a arduino?
You'd be better of using two 100 Meg resistors in series, which will produce only 0.25V instead of 5V, but you can then run that through an op-amp with a 20x gain.  You'd be drawing just 75 µA instead of 1.5 mA.

I originally suggested using a remote controlled (via GSM) relay to open the circuit when not in use, so there's normally no load at all.  But in retrospect that's not a good idea since with no load, 15kV will appear at the NO terminal of the relay, not a good idea.