My guess would be 30'
The oath of savagery can raise their reach 5 feet. A reach weapon another 5 feet. Enlarge doubles reach. 5 normal, 5 for holy reach, 5 more for glaive times 2?
Right distance but for the wrong reason.
An Enlarged medium humanoid has a natural reach of 10 feet.
With the use of the Oath power their natural reach is increased 5 feet to 15.
Then an appropriately sized reach weapon doubles the users natural reach (a small but important distinction) to 30 feet.
Always figure the users natural reach and then simply double it if they are using a properly sized reach weapon.
Also enlarge does not double reach it changes your reach to the appropriate natural reach for your new size. Another small but important difference.
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Weird. I had to go back and edit it and retype what I had posted.