This is a very good, and very tricky question. I'm going to give some scattered thoughts:
In undifferentiated cariogenic shock, norepi has been found to be an OK choice until the the cardiac process is identified.
A few questions first - did the patient have systolic or diastolic dysfunction? If the EF was 15% clearly there was a good bit of systolic dysfunction, as EF is preserved in isolated diastolic dysfunction (ie. the name HFPEF). Though this can happen with someone with diastolic dysfunction who has an MI or very late-stage, and can have management implications.
SO the objective of someone with systolic dysfunction GENERALLY is to reduce afterload and increase contractility. Dobutamine up to 5 mcg/kg/min does this nicely (at doses >5 you will increase afterload). Milrinone is also a good choice. Lower doses of epi can also achieve this. However you must be mindful that increasing HR will increase myocardial O2 consumption and decrease diastolic filling time (which is when your coronaries are perfused). That said, a heart rate of 80-100 is typically ideal in these situations with a drastically low EF.
HOWEVER, if your pressure is in the toilet (ie cardiogenic shock), you have to do what needs doing to increase your MAP or you won't perfuse your coronaries and will end up right back in Vtach arrest. It's a tricky predicament and I sympathize with you and your doc. Norepi in this case makes some sense because you will increase your vascular tone (aka SVR, aka afterload) to help perfuse your coronaries and will also give you some positive inotropy. Dopamine can also achieve this, and has the added benefit of increasing UO but is a much weaker drug than norepi or epi.
It is hard to justify giving lasix if someones pressure is in the toilet. I have seen people do it and augment BP with more vasopressors. There isn't any real evidence to support that, though. Also don't forget that lasix does have some (albeit minor) vasodilatory effects.
Some things that definitely help in these post-arrest very low EF patients:
1. Maintain NSR (treat afib, pace, amio, whatever you gotta do! Afib can precipitate another arrest)
2. Increase inotropy (basically any pressor EXCEPT phenylephrine will do this)
3. IABP, impellas seem to help
4. Target SpO2 about 90-92% (high O2 levels have been shown to decrease coronary blood flow at rates that thwart any myocardial benefit of having Spo2 of 100%)
NB: Vasopressors, by increasing diastolic pressure (and thus coronary perfusion pressure) tend to increase coronary blood flow)
Sorry this is so scattered!