Why is the Wallet 857 MB big?

Every other Wallets I have/had were about 20 MB.
yeah I saw that too. why is your wallet so big, its the largest wallet I have every used. I dont get it, if its just a JAVA file, we dont need 600 MB worth of data
This has been answered now a few times in previous comments. The proving keys are required for the wallet to function. They need to be downloaded either with or without the wallet but still must be downloaded. Doing it in one file seemed best. Please let me know if you have a quicker solution so we can work on implementing that for future users.
We are working on a native wallet that should resolve this in the long run.