Yes my dad had this issue but it was 2-3 years ago. He did ask in the chat if there was a limit of topup and they said that there is no limit. So he sent a large amount to cover a 3 month trip abroad and it was blocked by Revolut, they ask for proof of found, like a salary sheet but as he is retire he has no salary anymore. It tooks several days and hr end up to have to show a bank statement screenshot with a large enough amount to get it unfrozen. He said either you approve it or you return it and a close my account, and they approved it.
Not sure if it’s still like that now. You can ask in the chat support and tell them exactly that you will transfer 15k and confirm that no further verification is needed.
Otherwise you can use check on Monito.ch what is the cheapest way to convert the money in the currency you need, it might be cheaper than Revolut.