can i give 2018 mains exam in have completed my 12th exam in 2015 and i have completed this year diploma also
According, to the eligibility criteria of JEE Main 2018 you must have passed 12thclass or qualifying exam in 2016 or 2017.
To check the eligibility criteria you can check below link
JEE Main 2018 Eligibility Criteria
Good Luck!!