Postgrad student loan

Hi am a studnet in the UK, about to start a masters degree in september, at a different uni from my undergrad. I plan to do phd which means I definately won't have a full time job for the next 3 years. I applied to full amt of student loan thinking it worked the same as undergrad, and I thought the rates were the same but it turns out there different? I have enough money saved rn to pay off the postgrad student loan rn: does it make sense to just pay it all now? Or should I just not pay it yet, (my understanding is that it doesnt make financial sense to pay the undergrad one off asap)? Thanks, Russell