Trade-in iPhone XR now or after 15 series?

I’m gonna keep this short. I am planning to get the 15 Pro and want to get the max trade-in value of my phone. Would it be a bad idea to trade-in my XR to Apple for $145 or waiting until after the 15 Pro? I have a spare Pixel I would use in between the upgrade. I’m on T-Mobile if that’s relevant.