If it's been 20 years and you have not been on nicotine replacement the whole time, you are not looking for the "equivalent" of 1.5 packs per day unless it were 20 years ago.
You are looking for something that would suit a NICOTINE NAIIVE brain, at least to start, although I can say if you take to vaping, your tolerance to increased nicotine may rise more quickly as you start to vape, to your former levels. That may or MAY NOT happen.
I would NOT recommend disposables of high nicotine concentration like the Juul or the Blu, honestly.
Ideally, you could satisfy your nicotine craving with the lowest level of nicotine possible. So that means, if you get an AOI or pod device, you need to get one where you can add your own liquid, and start LOW like 1.5 or 3 mg/ml level. You may want to end up going higher but starting too high and lowering is kind of a recipe for artificially bumping your nic up to as high as you can go, and then lowering and having it be painful along the way.
I think it's good you are asking the question, but you kind of have the opportunity to start at 1.5 mg/ml which is REALLY QUITE low in such a delivery device, but you may wind up satisfied. If you don't it's a lot easier to go higher.
Just... don't forget the 20 years with no nic, at least SOME of your nicotinic receptors must have recovered or died off by now.
With that said, a Juul for example can go as high as 50-59 mg/ml. It's a weak power source sure, but I still got totally dizzy when I took a puff off my son's and I already VAPE 18 mg/ml and was a 3 ppd smoker.
I just hate to see you overdo what you may not need to overdo.
Anna