Very slow Macbook Pro Retina mid 2015

I have a mid 2015 Macbook Pro retina – has suddenly become ultra slow! And I mean unusably slow.

Have done all the usual things – SMC and PRAM reset – reinstalled the OS

The Mac is even slow and laggy when in recovery mode so I’m guessing hardware?

Blackmagic read/write speeds are around 150-200mpbs – Memtest checks out fine as does Drive DX

Could this be a logic board issue?