The current talent system is untenable. Once every 15 levels necessitates that they redo the tree every expansion as they are expected to deliver new talents at max level.
The easiest way they could add new talents for new expansion is keep the first 90 level talents, but add one talent every 1-2 levels for the new levels in the next expansion. This leads to talent bloat in the next next expansion unless they remove old talents again.
The old talent tree that lasted us 4 expansions was good. It is another example of don't fix it if it's not broken.