If you have control over the sensors you could transfer binary data which you could then Base85 encode like mentioned in this thread
But you also seem to have loads of decimal places, that just take up space and don't add value to your readings. If you can cut down on them, that'll be a start.
If you have no control over the source data, you might want to translate the incoming data on the Electron, encode that and then pass that on.
Or you just use a string compressor (e.g. <zlib.h>) and send that Base85 encoded again.