Most traditional Rubber Domes are limited to ~ 1-5 million clicks of durability if they're even listed at all
Rubber domes don't click. The word "click" refers to a click sound. A "clicky" keyboard switch emits a click sound, and so far all clicky keyboard switches have been mechanical. A click sound could also be emitted by electronics through a solenoid or a speaker, but then it wouldn't be a property of the keyboard switch.
The term you are looking for is "key press". You could also use the word "actuation" which implies that the key press has succeeded in being recognized electrically.
What other changes from traditional Rubber Dome KB construction is necessary to bring the KB up to the 15 million [key presses] level or better?
Maybe using a PCB instead of a flexible plastic circuit sheet?
Model M buckling springs have membranes as the actuation mechanism and often work fine for a very long time. I believe it is mostly when keyboards have been subjected to spills (coffee, tea, soda...) that membranes erode and break or short.
Topre and Model F buckling springs use capacitative sensing, which is contact-less and should last mechanically for longer but they are still sensitive to erosion and shorts.
Many types of keyboard switches will also worsen in feel a lot before they break. Topre rubber domes get stiffer. Regular rubber domes not only get stiffer but also a mushier landing.
Key Tronic used to have rubber dome/membrane keyboards called "Lifetime Series" because they had been engineered to last - but there was really nothing spectacular about them.