Hi,
ESI is not applicable to employees with total earnings more than 15000.
But there is an exemption to this rule:
There two ESI contribution periods: April to September and October to March.
And as per the rule, even if the employee crosses the limit of 15000, he will continue to pay ESI as long as he is within a contribution period.
Rule says:
"Provided that an employee whose wages (excluding remuneration for overtime work) exceed [such wages as may be prescribed by the Central Government] at any time after (and not before) the beginning of the contribution period, shall continue to be an employee until the end of that period ;]"
You can refer the act in the link below:
http://esic.nic.in/act.htm
Hope this helps.
Rijo