If you have 50 gallons in circulation, 1.5 gallons would be 3 % per day. This in no way compares to the benefits of the 25% weekly water change. For example, if your nitrates are at 100ppt. a 3% water change will only reduce them to 97ppt. On the other hand, a 25% water change would reduce them to 75ppt. Do the math on the 3% water change and see just how many days it would take to reduce your nitrates by 25ppt.
I did the math and it's definitely not my strong suit, but I think the difference is marginal.
Assuming 50 gallons of water volume with a starting point of 10ppm nitrate with 10ppm nitrate production per day, here's how the math broke out for me:
3% Daily
Day 1: 10 PPM
Day 2: 19.7 PPM ((10PPM-(10PPM x .o3))+10PPM)
Day 3: 29.109 PPM ((19.7PPM-(19.7PPM x .03))+10PPM)
Extrapolated to Day 8, you would have 64.005 PPM of No3.
25% Weekly
Assuming w/c is done on Day 7, on Day 8, you have 62.5 PPM of No3.
Day 1: 10
Day 2: 20
....
Day 8: ((70PPM-(70PPM x .25))+10PPM)
So at Day 8, you have 64 PPM vs 62.5 PPM