Hi Himanshu
while setting the SLA's there are few things that are to be considered.
1. Is the Ticket an enhancement or is it a bug
2. if this is an enhancement is it only Functional or is it having cross teams involvement like PI / ABAP or others.
3. If this is a Bug, is it an actual issue or is it caused by user mistake or lack of knowledge.
based on the above you can start the framework of SLA's
catergory 1 Bug
User Issue
Data issue
Knowledge issue - Provide Training
Actual Bug
High impact on business (can be done without ABAP)
High impact on business ( Have to get ABAP Correction done)
Medium Impact on business (can be done without ABAP)
Medium impact on business ( Have to get ABAP done)
Low impact on business (can be done without ABAP)
Low impact on business ( Have to get ABAP Correction done)
Category 2 Ehancement
Simple
Cross Application
Necessary - Legal requirement types - Urgent
Improvements - Not Urgent but required
Nice to have - Not Urgent, Not Necessary.
I hope this will give you some starting ideas 
-Cheers,
Sachin