Is there a memory leak or something when i load textasset from AssetBundle

1.The project compression method is "LZ4"
2.There are some different assetbundles in streamingasset，"storyconfig1" is small asset,contains a JSON text of 3M size,"storyconfig","ccc" and "ccc1" is big asset,contains json text of 18M size
3.Here is the test interface I used to read the different configurations
My question is when I read 3M text from the Bundle, I can reclaim Mono memory, but not 18M.
Is my Unload method incorrect?

Unity version is 2018.4.10

 

I can recycle the Mono memory added by reading 18MTextAsset if the compressed format is the default, although there are other issues such as the memory cannot be freed clean after repeated reads.

 

I've seen different performance on different phones, and in my tests on the MotoG5, the memory leak was worse than on other devices