@model BTCPayServer.Models.ServerViewModels.RatesViewModel @{ ViewData.SetActivePageAndTitle(ServerNavPages.Rates); }
BTCPay relies on Bitcoin Average for getting crypto-currency to fiat rates
If you want BTCPay rate cache to be smaller than 15min, you should register to BitcoinAverage and get a paid API Key.
If your BTCPay server instance supports lot's of merchant or is used a lot, BitcoinAverage will rate limit your server, and invoice will be created using less accurate rates. (From Bitpay)