You are confusing charging with speed of charging. The ability to charge your Macbook Pro is only a function of common charging protocols. A 45W speed of charging will come with some downsides, such as cost and efficiency (you would get less actual total recharge).
I just did a quick 2 day business trip and used a tablet which a 15W recharge input, but I used a 10W recharge input, because it was lighter and cheaper, I plugged it at every opportunity when stationary and it did that perfectly fine. I am about to do 2 more 2-day business trips, total of 30 hours of flying and living out of hotels and a lot of moving, so tablet, phone, BT buds and a Powercore and a Powerport. The 45W chargers are larger. Everything bulks up, cables get thicker, chargers get bigger, portable charges become more expensive and larger as you increase the Wattage.
Where I would not want to skimp on is the Wattage of a multiport Powerport, to gain the maximum benefit of any brief time near a wall socket, and on the recharge speed of a Powercore.
If I were to own a 45W input device, if there was say a 30W output charger which was cheaper/lighter, I'd give it serious considering.
Speed = you didn't really think about it earlier enough did you.
I have a trip to the USA southeast late next week, just where Irma is predicted to be, plan for the worst, hope for the best, power cuts and a 26800mAh Powercore and a LC40 torch, and lots of dry bags, I think.