Using a three-wire cable across two breakers
DANGER!
This is totally wrong. You have 2 pairs of 1/2-size breakers - a.k.a., &quot;double stuff&quot; or &quot;tandem&quot;. If you measure voltage between black and red (i.e., between a pair of hots) you will find 0V instead of 240V. If this was done by an actual licensed electrician, he should have his license revoked. If it was done by a handyman-acting-as-electrician, this is why most places don't allow that.
Note that this would be perfectly fine with two separate cables - i.e., each breaker getting its own black &amp; white wires. But sharing (MWBC) only works if the pair of breakers are (a) on opposite poles/legs so that you get 240V between the hots and (b) the breakers are physically paired (handle tie or double-breaker) like the 40A pair across from these breakers.
And now for the really crazy part. The usual reason to go for 1/2 size breakers is because you don't have enough space to put full size breakers. But you have more space right below above (picture is upside down, or panel is upside down) the new breakers! You could easily have 2 pairs (i.e., 2 double breakers) of 15A full-size breakers and everything would be just fine.
There is actually one other alternative. A quadplex breaker:

The beauty of a quadplex is that the inner and outer pairs each function like a traditional double breaker. Red and black to the outer breakers + white neutral. Red and black to the inner breakers + white neutral. Done.
Difference in cost between 1 quadplex and 2 tandem breakers at Home Depot? Less than $11. Probably even less of a difference at an electrical supply house.