It is a bit worse than original PS1 games too, mostly because those games were made with the limitations of the disc based storage system in mind, and therefore had data such as the main menu stored in RAM at all times. FF4-6 however, which were programmed with a cartridge in mind, did not attempt to do that at all, because the game assumed it would get instant access to the data needed without access times worth mentioning. With a disc and considerably slower access times, that wasn't possible, but the game wasn't modified to take that into account.
While this is mostly guesswork based on newer sorts of storage types similar to what cartridges used, I would say that access times for a SNES cartridge could be as low as a millisecond (modern day SSDs can get below 0.1 ms). Compare that to a modern day hard disk, which are still at around 8-14 ms, and a 1x CD drive (found in the PS1) which has got at least 150 ms (that's a theoretical minimum, in many cases it could be more than 300 ms).
While a few milliseconds doesn't seem all that slow to most people, you gotta remember that it's 150 milliseconds *each time* the game needs data that isn't prefectly lined up after the previous chunk of data it needed. This quickly adds up to quite a bit of time.