I'm surprised that the laptop is handling it okay, but it's likely due to the Intel QuickSync on that computer that is helping to decode the H265 media.
Basically, H265 is one of the hardest video codecs out there to decode (play). I personally won't even work with H264 straight, let alone H265. You have 4k, high framerate, in one of the most difficult possible video codecs to work with so it's honestly not a surprise at all that it's lagging. You should consider making low-res proxies into an edit-optimized video codec like ProRes 422 Proxy. Otherwise you're just in for a very painful slog with that kind of media.