Chunks won't load or load VERY slowly on my world, and it has become VERY laggy!

Preamble:  My world has been working great, but, over the last 4-5 days, the performance has plummeted and this "lag" has become unbearable!

World Statistics:  My world is about 4 years old.  It was previously converted from Xbox One Edition.  It is Survival only with Achievements enabled, and the world is on a Realm!

Lag examples:

• Entering/exiting the nether is very slow
• Chunks refuse to load or load VERY slow when walking, running, traveling in a minecart, or flying.
• Livestreaming via Xbox streaming apps increases all of these lags (making streaming impossible while playing on the realm)!

Additionally:  This lag became massively worse over the last 4-5 days...  We have not changed any settings for the world in that time!  The only thing I have done in that time-frame is:  travel in the nether and install a Blaze xp farm which is DISABLED and not spawning any mobs.  So the biggest change was installing some small structures in the Nether and traveling a bit in the Nether.

Also:  We use elytras to fly around our world normally.  We also use fireworks to extend our flight.  BUT, the chunks won't load or load VERY slowly! and this makes flying impossible without having to close the game or getting stuck in an unloaded chunk!

Please help!

Thank you so much!