XP in Escrow

One of the things I am finding annoying in 5E is the level advancement table. It is just too fast for my tastes. I'm a believer that players should have time to experience and develop their characters at each level, and as a DM I like being able to make use of the great number of things available for characters to encounter appropriate to each level to build an early sense of wonder.

I have some other beefs that are waiting their turn to be discussed as well, however, this time it is the rapid rocket level advancement.

To give you an example from play in CaptCorajus' game, here is what the party has either defeated directly or avoided intelligently (both should provide experience points), in  recent play:

Lich (CR21) = 33,000 experience

Death Knight x2 (CR17) = 18,000 xp each = 36,000 experience

Iron Golem (CR16) = 15,000 experience

Minotaur Skeleton (CR2) = 450 experience

Skeleton Archers x12 (CR1?) = 200 xp each = 2,400 experience

Flaming Skeletons x2 (CR3?) = 700 xp each = 1400 experience

So, guesstimates totaled = approximately 88,250 xp divided by 4 characters is 22,063 experience each.

The party had been blowing through levels fast, but now we would nearly double our xp total and that would have landed at 48,563 (49,563 for the dwarf), which would blast us over 8th level and into 9th level. The Capt only allotted us 6,000 each which puts us below 8th level. 

The experience awards seem higher than they should be, and when combined with the level advancement requirements (300 points to get to second level?!).

I'm sure there are better ways to to handle xp and advancement that can be whipped up for home games.

Meanwhile, that leaves us with the question: Are we collecting interest on the xp sitting in escrow?