InstrumentChecker: Investigate running times

## Where?
Instrument checker now takes over an hour to run, it should probably be quicker

## Reproducible?
Yes, shows in current tests

### To Reproduce
- see tests on jenkins

## Acceptance criteria
- [ ] cause of instrument checker long running time identified and fixed

## How to Test
_verbose instructions for reviewer to test changes
(**Add before making a PR**)_