Mach Number and Stall Speed
Although the aircraft Mach number is relatively low, that doesn't necessarily mean that the Mach number in the accelerated flow near the leading edge is equally low; you can start getting Mach effects on stall aerodynamics at surprisingly low speeds.
On "our" products - which admittedly are swept wing, which the subject at hand isn't - we see an effect on stall angles and CLmax starting at M0.20 or earlier. It's not a minor effect, either - the stall angle can reduce by as much as 25% by Mach 0.30-0.35.
It all rather depends on your stall mechanism; if you're tripping the flow artificially you'd expect that to conceal any (or at least some) Mach effect. If you've got a completely clean natural stall then you will likley see something.