Sadly this is the conclusion I've come to as well.
I drank the BIML Kool-aid years ago and we designed our whole Data Warehouse with it. But keeping VS2015 installed just for this is painful.
I know their answer will be to buy BIMLStudio but I can't shell out that kind of money just for this one project.
Even if BIMLExpress was a cheaper paid license I'd probably pay it even for the limited functionality but to dangle BIMLExpress in front of us in it's current (unsupported) form is just cruel.