Rodion,
As Bob described, it’s possible to use U.3 SSDs for editing, in a RAID form, inside a NAS.
For your use case, using one 15TB $2000 U.3 SSD may be overkill.
A U.2 or U.3 SSD will deliver that speed only if the interface supports it. Like if it’s installed on a PCIe card, or directly in a U.2/U.3 compatible slot internal to your PC.
If you’re on a Mac, you’ll need to be using a Thunderbolt to U.2/U.3 adapter of some kind (OWC makes enclosures which are U.2 SSD compatible). Used in this manner, a U.2/U.3 SSD will work at about 2,500-3,000 MB/sec which is fast enough for 8k video file processing. But then these speeds are also achievable with M.2 NVMe SSDs.
You could also take a look at Iodyne which makes SSD based storage which can be connected to multiple Macs simultaneously.
Also, bear in mind that U.2 and U.3 in some situations/enclosures/adapters are not interchangeable.