If it's anything like the PS4, you might be able to fix this by running a HTTP proxy using Squid and configuring that on the PlayStation. There's something really funky about Sony's networking on them, and configuring a squid proxy for my PS4 vastly sped up my downloads.

I tried to find an article covering this but I've had no luck, so I'm just going off memory here, but I'm pretty certain that's all that was required.