Here is what the recall states:
Recall - Spare Tire
To: All Jeep(R) Dealers
Safety Recall # 757 -- Spare Tire
1996 Model Year Jeep Grand Cherokee (ZJ) Vehicles Equipped With a Quadra-Trac 4WD Transfer Case (Sales Code - DHR) and a Compact Spare Tire
Installing the compact spare tire in either a front or rear position on about 65,000 of the above listed vehicles, may cause front axle damage and/or a vehicle fire. To correct this condition, the compact spare tire must be replaced with a full size (conventional) spare tire and wheel assembly. The new spare tire and wheel assembly will NOT match the other tires and wheels on the vehicle and is still intended for use only as a spare tire.
What my Jeep got outfitted with as a full size spare under this recall is a 245/70R15. What came with as factory issue is the 225/70R16.
Comparing the tires, I find that there is 0.36% difference in the tire diameter between the two.
When I compare your 225/75R15 to the 235/75R15 I see that the 235 is 2.05% larger in diameter (28.28 inches vs. 28.87 inches) or about 1/4 inch in radius.
If I were in your place, I wouldn't worry too much about it, but by the same token, if I had to use the spare, I would endeavour to get it repaired ASAP.