First, to clear up some terminology: a "mega backdoor Roth conversion" is generally referring to the conversion of after-tax, traditional 401(k) money to Roth. If you have this type of money, you should definitely convert it to Roth as the traditional after-tax bucket is a worse place to leave your money for the long term than Roth, and converting is unlikely to have much effect on this year's taxes.
If you have pre-tax traditional funds in your IRA, a Roth conversion would require you to pay tax on the entire sum this year. Probably not what you want to do! This type of conversion is also not typically called "mega backdoor."