I have been bulk aging in carboys anywhere from 10-15 months. Are you saying I’m wasting my time and should just bottle after six months in glass?
Winemaking is an art, not a science. If it was science, we could make calculations and produce a great wine every time. But we can't -- every wine is different and we (winemakers) must make judgment calls based on each unique situation.
IME wines go through a lot of chemical changes in the first 4 to 12 months. Lighter wines (less body, acid, sugar, tannin, etc.) complete major changes sooner as there's less "stuff" to go through changes. Heavy reds need more time in bulk, as the changes take longer to progress. Note that I didn't say "complete", because no wine ever completes changes. Wine changes continually until it passes drinkability (in human opinion).
Giving wine time to "mature", e.g., complete major changes, prior to bottling is a good idea. I've proved to my own satisfaction that bottling early produces unacceptable bottle variance (in plain English, some bottles were crap).
Beyond a year old, most wines are ready to bottle. There is no advantage in further bulk aging in a neutral container. Sediment has dropped, the wine is clear, and aging in smaller volumes produces quicker results.
Barrel aging is different. The non-neutral nature of the container makes a difference. My barrels are neutral (no remaining oak character), but the evaporation effect (10% volume reduction per year) produces a tremendous difference in the wine.
Based upon my experience, there is no significant difference between 11 and 15 months in a carboy. However, if you're happy with your results, keep doing what you' re doing.