Move files from Account A to Account B 165 GB data

I’ve been using Microsoft Office 365 Family for several years, sharing it with my family members.
We have 6 accounts, each with 1 TB of storage.

One of my accounts has now reached 985 GB, so I need to transfer files from Account A (my account) to Account B (my wife’s account). These files mainly consist of photos and videos — over 200,000 files in total.

I tried transferring a 6 GB wedding shoot (.ISO format), but it took more than an hour.
Re-downloading and uploading all the data isn’t feasible as my internet connectivity is limited to 100 mbps only.

I’m looking for the best and most efficient way to move these files directly between OneDrive accounts.