timeline lagging hard even with proxies (please help)(im going insane)

I'm editing 4k footage from a DJI Action 5 for a client. I've converted the .lrf files to proxies and I have the playback resolution set to 1/8 but my timeline is lagging so hard it's basically non-functional. I'm working off an older computer (macbook pro 2015, 2.9 Intel core i5, 16gb ram) so I'm sure that's part of the reason, but I've definitely edited 4k footage on this before and haven't had this bad of a problem. Why is it lagging so terribly even with the proxies turned on? What can I do to get to a place where I'm able to work with this footage. I'm upgrading to a new macbook pro next week but this video needs to be done by this weekend. Please help!!