Do we any encryption turned on or anything authentication enabled on SSID?
If the devices specific to Android or IOS we could block by configuring DHCP finger printing else we may need to relay only on ACL.
You could try blocking some of the chatty protocols SSDP, upnP,netbios traffic or on the air which would help in increasing WLAN performance
see for below example.
user-role <wireless user role name>
session-acl deny_mDNS_acl
session-acl deny_SSDP_and_UPnP_acl
session deny_netbios_acl
session-acl deny_client_acting_as_server_acl
session-acl allowall
else simply enable the broadcast filters from VAP profile which wuuld drop the B`cast/M`cast on air however still arp,dhcp,VRRP will go through.
configure terminal
wlan virtual-ap <profile name>
broadcast-filter all
broadcast-filter arp
Thank you,