"If you're experiencing sluggish charging with your iPhone 15, there are several steps you can take to improve the situation. Firstly, due to the open nature of the USB-C standard, you have the flexibility to use almost any USB-C cable you can find, including those labeled for 'Android' phones. While the iPhone 15 comes with a quality woven cable in the box, feel free to experiment with other USB-C cables you may have.
However, if your iPhone seems to be charging slowly, it might be worthwhile to consider changing your charging adapter. In the past, Apple used to include 5W power adapters in the box when accessories were provided. If you still have one of these, it's safe to use with the iPhone 15; just pair it with a USB-C to USB-A cable. However, keep in mind that it will charge your phone at a modest 5W rate. While this was sufficient when smartphone battery capacities were smaller, today's iPhones boast much larger batteries.
Consequently, charging at 5W could take four or five hours to reach a full 100%. To speed up the charging process for your iPhone 15, you'll need a higher-wattage charging unit. Although the iPhone's USB-C port technically supports power up to 27W, efficiency tends to decrease above 20W. Therefore, using a USB-C cable with Apple's 20W USB-C power adapter can charge your iPhone 15 from 0 to about 50% in approximately 30 minutes and from 0 to 100% in less than 2 hours.
However, you're not limited to Apple accessories. There are numerous third-party high-wattage USB-C charging options in the market that may offer more convenience than Apple's adapters. Using power adapters exceeding 20W is safe, as they will charge your iPhone at its maximum supported speed. For instance, if you have a USB-C MacBook power adapter, you can utilize it to charge your iPhone at full speed. Connecting your phone to one of the MacBook's USB-C ports, while it's connected to a power source and charging, can also provide a nearly full-speed charging experience."
