5e - Slowing advancement after Level 10

The 5e XP table is designed to speed up advancement after level 10. Discussion on doing the opposite here for a megadungeon sandbox campaign with PCs of various levels. Conclusion is that simply halving XP awards to level 11+ PCs should work best, giving the following effective requirements:

10 to 11: 21000 > 21,000 XP as per RAW
11  to 12:15000 > 30,000
12 to 13   20000 > 40,000
13  to 14  20000 > 40,000
14 to 15   25000 > 50,000
15 to 16   30000 > 60,000
16 to 17   30000 > 60,000
17 to 18   40000 > 80,000
18 to 19   40000 > 80,000
19 to 20   50000 > 100,000

Going Epic-10 in 5e D&D

I suggest to DMs that if they are running a story-based, low combat game in a lowish-fantasy setting, then go “E10” – levels should be capped at 10 not 20, and use the Epic rules in the DMG from 10th level: every 30,000 XP above level 10, a PC either gains +2 attribute (I’d retain cap at 20, maybe 22); or if the game uses Feats the PC can gain a Feat of the player's choice.

Character Advancement
Experience Points Level Proficiency Bonus
0                               1                +2
300                           2                +2
900                           3                +2
2,700                        4                +2
6,500                        5                +3
14,000                      6                +3
23,000                      7                +3
34,000                      8                +3
48,000                      9                +4
64,000                    10                +4
94,000                    E1               +4
124,000                  E2               +4
154,000                  E3               +4
+30,000                  +1               +4

Edit: The Primeval Thule 5e setting seems particularly suitable for this approach.