This coincap.io the price changes every second. Its real-time even in coinmarketcap, if you just refresh it the price keeps changes not every 15 minutes, all the time. But why do you need the 15-minute interval? The market price changes every time since we all bid for the price not just to BTC but other altcoins.
I am looking for the price change percentage (this is the last column on the site that you provided). Rather than the 24hr change, I would like to view the 15 minute percent changes for currencies. This is a great way to spot breakouts before the real FOMO kicks in.