NH-D15 is no better than at least half a dozen other top cooler, like PH-TC14PE, R1 Ultimate, Le Grand Macho RT, Silver Arrow IB-E Extreme, Dark Rock Pro 3, TRUE Spirit 140 Power, etc., and these are often lower priced.
First off, don't confuse all AIOs with CLCs. AIOs are All in One liquid cooling that at present time include 2 kinds of pre-build and filled liquid coolers; AIOs that are CLCs and AIO that are not CLCs. CLCs are assembled is ways that meke them near impossible to repair with no way of topping off coolant. Almost all CLCs are made by 2 companies; Asetek (who owns the USA patent rights to LCLC and CLC concept of a pump mounted on waterblock) and IDCooling. There are 2 basic low cost pump designs that are basically the same flowing about 40-60 liter per hour coolant through low cost aluminum radiators that require high airflow to cool well. By comparison the pumps in AIOs flow significantly more coolant, use copper radiators, threaded fittings, fill port and are much better made. Swiftech H series pumps flow up to 660 liter per hour and Alphacool OEM AIO pumps flow 72-100 liter per hour. Alphacool OEM are their own Eibear, Fractal Design Kelvin and be quiet! Slent Loop.
As a comparison the D5 pump (arguable the most popular custom loop pump) flows up to 1500 liter per hour.
In all honesty there have has been little to no improvement in the most commonly sold CLCs . They depend on different looking pump covers, fancy fans, and other bling to promote new models. People jumped on the CLC wagon because they were able to have 'water cooling' without really understanding that the only thing CLCs and real water cooling have in common is 'water'.

Many who still push the CLC hype do so with no understanding of how much different and better real water cooling is. Many think airflow ratings are key to how well a fan performs when the reality is fan pressure rating is more important than airflow rating ..but that's another story.
A good air cooler and case fans cost less than a wonky CLC, will cool better, will be way more dependable, will be quieter, and the only thing that might go bad in 5-8 years is the fans and they can be replaced without braking the bank.
Short version; Get a good case, some good case fans and an air cooler to "Live long and prosper."
