... that's why we have one!
Only four months into it, but from the start, we've been riding longer distances than we did together on singles, and of course I get whatever workout I feel like achieving. She too is now putting in more effort, enjoying the bike's speed relative to her on a single and up for riding the tandem as often as we can. Now I'm down to riding a single just two-three times a month when our schedules can't mesh.
Our only regret is that we did not get one sooner. So if you both enjoy riding now, and your lifestyles can accommodate it, maybe you don't need to wait two years to explore the fun?