It depends on what they expect their marginal tax rate to be once SS and any pensions are on line and what it is now. We don't have enough info to know. Commonly, there is a time between ER and once SS and any pensions start that people are in a lower tax bracket and that is the opportune time to do Roth conversions.
Our conversions are a mix of 0% (covered by part of our standard deduction), 10% and 12% and have averaged 8.5% over the last 7 years... compared to 28%+ when we deferred that income and 22% once SS and my pension are going. Assuming 22% later in life our Roth conversions have saved us $50k over the last 7 years.
During that gap time, Roth conversions are low hanging fruit.
I did assume there were no pensions since non were mentioned.I did go back and recalculated and the total tax deferred they have is $586k. So let''s assume the grow 7% a year as they are invested conservatively. They will then have $770k, although they may be spending
down now so maybe less. Average RMDs over the first 10 years is 4%.
And 4% times $770k is $31k, added to SS of I'm guessing $30k.
$61k minus $24k (standard deduction) = $37k of taxable income, but, I don't think they will even be taxed on their SS because,
adjusted gross income + nontaxable interest + half of your Social Security benefits will be below $32k. That $32k has it's own yearly inflation increase, so it will be higher when the RMDs start.
It also matters if one of them dies early and pushes the other into single filing status with lower income tax brackets.
I hope I have listed enough to get the OP thinking about what to think about when making this decision. My gut feeling with only the details the OP has given is, it may cost them more if they do Roth Conversions then if they don't. But longevity and the single filing brackets needs to be in that calculation.
If the OP wants to add more info, like SS, pensions, and are you spending down your tax deferred accounts, others smarter than me can give better advice.
Now I'm going to go kick myself again, because I think I could have done a $60k+ Roth conversion and stay in the 12% bracket for 2019. This is our first full year of retirement so I need to get it figured out myself. I do have concerns RMDs pushing me into a higher tax bracket in about 8 years.