Imagine if this was a lot of money. This has made me feel concerned using btc for big amounts.
It's clear that your fault makes your transaction really slow to get confirmed due to the low fee. You should check the current fee/bytes first before sending to make sure your transaction's fee wasn't below the current requirement. Even if you send 500 BTC at the same time if you give above of the current requirement fee your transaction will be confirmed fastly.
Though, honestly, I've made a mistake about setting up low fee same as you which is 0.0001 recently and luckily got confirmed within ~30 hours, my bad indeed.
For another time, I really recommend you to use some sort of bitcoin wallets that have a feature to set up the requirement fee automatically.