I think the compounding interest difference between a 6.5% loan and 401k contributions is pretty likely to be a wash, which is why I'm focusing so much on the tax implications instead.
One thing that has helped me in the past is to calculate the amount of interest paid if I paid something off in 1, 2, or 3 years. Oftentimes, the difference in actual dollars isn't massive and it helps me realize that the right decision might just be whatever helps me sleep at night.
With that in mind...
If you're in the 22% tax bracket & can still pay off the loans in a year, I think both of you contributing 15% to your 401k's is a pretty reasonable place to draw the line. You might check to see how close that gets you to the top of the 12% bracket too--if you're close it could be worth throwing a little more in the 401k to stay there even if it delays paying off the loans by another month or two.
Additionally, up to $2500 of the student loan interest is tax deductible if your joint AGI is below $140k. So that makes the effective interest rate on the 6.55% loans only 5.764% in the 22% tax bracket. Again, use your 401k contributions to make sure you get below this cutoff.
One last thing to consider: did you get a partial stimulus check (between $1-$2400)? I did, so I am contributing more to my 401k this year than I had originally planned. The check was based on your 2018 or 2019 AGI, but if your 2020 AGI is lower you'll get an true up on your 2020 tax return. It effectively gives you a 5% credit for any reduction in income between $150,000 and $200,000 if you are married filing jointly without dependents.
Lots of things to consider & if you're not a tax nut like me it may sound a little overly complicated. Again, I think 15% each to your 401k and then pay off the loans is a totally reasonable line in the sand--just some other food for thought if you want to really optimize everything.