Select Index Change Event get Fired Every time as country select from dropdown

Question

I have dropdown that is filled by country
on selectindexchange of country it populates city dropdown
 
as user change country from dropdown selecindex event get fired every time to
populate city 
 
it occurs 10000 times per day ( some time server takes 30 sec to 1 min )
 
is there any solution to controll selectindex change event of dropdown every time ?
or any better solution ?
 
thanks