That wasn't it, but it sent me on the right path.
main.lua is no longer in use, and I have removed it from github.
But adding loads of debug-prints made me aware that my function GetItemStats (which parses and consolidates the SavedVariables table) was being called lots on load. Turns out GetItemStats is a builtin function of WoW which I overwrote...
After a small namechange for the function, the addon stays @ ~1.5MB.
Thx for your help