Your bottleneck is the USB stick and USB 3.0 itself. There's simply not enough bandwidth to get smooth playback.
From your specs (quad i5, 1.4 GHz) I'm guessing you've got a the 2019 13" MBPro which should be powerful enough to handle quite some video editing, so I'd highly recommend getting an external SSD connected via Thunderbolt 3, or at least USB-C. While USB-C is optically the same plug as Thunderbolt 3, the protocol and speeds are different. Thunderbolt 3's max throughput is about 4x of what USB-C can handle.
For maximum performance get a NVMe SSD (M.2) drive and a Thunderbolt 3 enclosure. You can get 1TB with case for ca. 250 USD and the maximum throughput is just as fast as the internal drive (same technology), up to 1400 MB/s which should be enough to even edit 4k footage.