Why is verification using DSA slower than verification with RSA?
If you compare DSA with SHA-256 and a 2048 bit group modulus $p$, to RSA with SHA-256, a 2048 bit modulus $n$ and public exponent $e = 65537$, on you will at least perform the following operations:

DSA


$g^{u_1}y^{u_2}$ - 2*256 squares $\mod p$, up to on average 2*128 multiplications $\mod p$, depending on implementation optimizations.


RSA


$s^e$ - 16 squares $\mod n$, 1 multiplication $\mod n$.