which cable to use to connect two thunderbolt4 Mac book pros

2015 MacBook Pros have Thunderbolt 2 ports. Those used Mini DisplayPort connectors. Thunderbolt 3 and 4 live on USB-C connectors.

So if you were trying to make a Thunderbolt connection – to use Thunderbolt Target Disk Mode, or to set up an IP-over-Thunderbolt network (Thunderbolt Bridge) and do network file sharing over that, you would need roughly $80 in Thunderbolt connection hardware:

• Apple Thunderbolt 3-to-2 adapter ($50)
• Thunderbolt 1/2 cable ($30?)

It might make more sense to buy a USB 3 flash drive, hard drive, or SSD, and use that to move the files.

Just the other week, for instance, a local store had credit-card-sized 1 TB SSDs on sale for ~$60. USB flash drives with 32 – 128 GB of storage can go for under $20 on sale.

With the Thunderbolt adapters and cabling, if you only use those once, you might be kicking yourself for spending $80 for that one-time transfer.