Wallet is slow with 200k subaccounts
Reported by Antidarknet:

> the official wallets are extremely unstable at 200,000 subaccounts if each has had at least one transaction in and one out. Try generating more subaccounts after 200k it takes many times longer to generate rather than when first initializing a wallet. The more accounts you add the slower it gets. Should probably fix that too. Don't take our word for it but test it yourselves.
