The HSRP multicasts per vlan are a function of
1) The number of vlans
2) The HSRP timers standby timers
3) If you've defined 1 HSRP group per vlan, or configured 1 HSRP group only.
I assume you have a separate HSRP group per Vlan.
If so, check the HSRP timers, hsrp groups, calculate how many broadcasts you should see & compare with normal broadcast levels.
Cheers, Ian.