Bill makes a solid point with his comments.
One aspect to add is that the purpose and circumstances when wearing one of your Hublots vs adorning your wrist with a 15202 might be very different.
The natural habitats aren't exactly the same, and adding the 15202 would definitely add true elegance (apart from adding one of the true and tested timeless classics) to your nice collection of watches, currently covering a spectrum from casual to sporty, to keep the categories simple. The 15202 perfectly does everything from (smart) casual to formal - you're always well dressed with it.
As for the pricing and keeping its value, I guess trying to find a cheap second hand 15202 will prove a to be a challenging task and might just about answer your question in these regards.
Sacrificing two watches you seem to have grown out of in order to obtain one that will open up a new spectrum along your journey with timepieces is a fair deal and makes the new addition all the more emotionally rewarding.
Reasons for the pride and joy of owning a 15202 you will find aplenty around this forum.
You didn't choose to part with the Hublots for no reason.
As an alternative, keep the one you feel is more special to you and sell the other one while trying to get hold of an 15202...
It's all about the journey and the quest - enjoy the ride!