internet connection problem "internet cafe with 65 computers"

i have 3 internet connection here, and all of them are cascaded to each other, i have 2 hubs and 3 routers and modem, each of my internet connection has a speed of 3.5mbps and also i have 65 computers. now here;s my problem even though i have 3 connection and divided each connection to my 65 computers im still experiencing slow internet connection, when i tried to ping a certain site using each line i am recieving 800–1500 ping reply. is there any problem regarding my connection?