An add-in 100mA current limiter for debugging could be quite simple - use the classic OPAMP + N-MOSFET constant current sink circuit for the -15V rail, and its P-MOSFET mirror as a constant current source for the +15V rail, All its going to need is a dual rail to rail OPAMP, the MOSFETs on a small heatsink, a couple of Zeners for Vgs clamping and a few passives.
It will spend most of its time with the OPAMP outputs stuck at opposite rails as it tries to turn the MOSFETs on harder to increase the current, but when you hit the limit, after a very short surge while the OPAMP output unsticks from the rail and starts slewing hard towards the MOSFET Vgs threshold voltage it will cut the current back to its limit. Foldback limiting could be added with an extra resistor from each OPAMP output to its control voltage (in+) input (from a resistor divider between the rail and ground) to cut back the commanded current once the output has unstuck from the rail, sized so it never takes the commanded current below say 10mA.
Even some 50mA polyfuses, + clamping diodes so you cant drag the + rail below ground or + rail above ground would probably save your day.