SEER on only 1 piece of equipment is not very meaningful. The combined SEER of the outdoor unit, coil size, and blower (air handler or furnace) is what really matters.

For example, a described 13 SEER outdoor unit can be matched with a particular coil and blower and rate a higher SEER.

In addition, the individual pieces are often described as a particular SEER for the entire equipment family, from 1.5 to 5 tons. And again, it is the SEER of the system matchup that matters.

If you have paperwork from your purchase with a AHRI rated SEER, you can go to the AHRI website, and look it up. Every matchup will have a AHRI number.

Here is a link that might be useful: AHRI Directory

juliekcmo is right, many condenser units have range SEERs, it may be 14 or 16 depends on the match components (coils, etc.)

Don't forget seer can also go the other way if the system isn't matched. A 15 seer outside unit with an unmatched coil or inside unit can drop considerably.