The 15" TRX rims are 5-1/2" wide, which is a good width for our cars, but you need a tyre with an outside diameter of something very similar to the original size in order to avoid clearance problems under the front of the car.
The 185 width is a good size for both a 5-1/2" wide rim & for the car, so in order to get a 185 tyre in a 15" rim fitment, that comes close to about 550mm to 555mm diameter, the calculator says it needs to be 185x45x15 & this results in an OD of almost 550mm.
I don't know if this size even exists, but if it did, i don't think it would be particularly cheap.
Another alternative would be 175x50x15 which gives us 556mm, but once again, i don't know if that size even exists.
The most cost effective, & practical size is a 185x60x13 tyre on a 5" or 5-1/2 rim for front use. Anything wider usually means that you have clearance issues as there is not a real lot of room in there. This tyre size is readily available & very reasonably priced.
Your Stanza rims fit this size criteria, but they have too much negative offset [the rim sits inward too far]
If you find a set of rims that you think might be good, measure the distance from the wheel mounting face to a line across the back edge of the rim. You will need a rule & a straight stick. If this distance measures very close to 4" [100mm] then your'e in. The Stanza wheel measures 4-1/2" [112mm] & this is where the problem lies.
I have no idea what the 15" TRX wheel measures out to, but it doesn't look to be a good choice.
For rear tyres, i would suggest either 195x60x13 or 195x65x13, however the car would benefit from a 1200 engine if you go to these larger sizes as they increase the overall gear ratio & make the engine work a little harder. Sort of like an overdrive.

Both these cars [above] use 13x5-1/2" or 5" rims. The sedan on the right uses 185x60x13 tyres, but the coupe on the left doesn't & had dramas every time he hit a bump or turned a corner. The sedan never had a problem, even after mild lowering.
It's the outside diameter that will suck the fun out of it if it's too big.