Instantaneous ?
Don't think so.
A shame the Spark controller is no like the M1P, with telemetry, including RPMs.
You should be able to do a flight, with tests, pauses, another test etc, and get the info from the flight log(s).
Are RPMs in the .txt flight log, via phantomhelp or Airdata ??
Probably not, can't recall.
They would be in the .DAT file (on the Spark internal memory), you can decrypt that using
DatCon apps
You can find them via the instructions there, download the apps etc.
You can use CsvView, Excel, etc to view these.