You are correct, it's a little confusing but the
15640 is listed as fitting the 1998 *only* Accord EX with 2.3L, and of course 98-02 3.0L V6
That being said, the 15690 will also fit the 98 2.3L.
I will add the fitment info from the manufacturer.
The 15690 fits the 98-2000 EX, LX, DX and SE...