As is typical for 103 engines you are on the ragged edge of HC at 15 MPH. The 25 MPH numbers are always better because the converter heats up during the 15 MPH test. Given the relatively high level of oxygen there is definitely room for improvement to reduce both HC and CO, and the hotter the converter the better it will oxidize HC and CO.

Frankly, with the level of O2 you have I'm surprised it passed. It's common to be at or near the HC limit with a tenth or two percent of O2. The fact that you have relatively high O2 and reasonably low CO indicates a good mixture, and no adjustments are necessary. For your next test make sure the converter is as hot as possible.

Always drive the car for at least 15-20 minutes before the test, preferably with a freeway run. Go to a "drive through" test establishment at a time when there is no line so you can get right in. Prior to turning the car over to the tech, keep the engine running at 2000 revs in neutral with the defroster on so the A/C compressor puts some load on the engine.

If possible, go on a rainy day and ask them to run the "tire dry procedure". They will run the car on the rollers with no load at 2000 RPM for about a minute, and this will heat up the converters.

The 103 engines are typically near the limit, especially at 15 MPH, even in perfect adjustment and operating order, so you have to "manage" the test procedure to ensure that the converter is as hot as possible when the test begins.

Duke