As of the Gates of Discord expansion the capped mana regeneration from worn items is at 15. And the capped hit point regeneration from worn items is at 35. All of them stack.
There is talk of them raising the worn mana regeneration cap in Omens of War since it has been at 15 since Velious when you could only get ft 1 and 2 using the highest quests and raids and now still is 15 when anyone can twink their lvl 1 alts with about 4 or 5 ft for minimal cost. Hopefully the health regeneration cap will go up a bit too in proportion...
Liveye (lvl 65 Wizard)