I did some quick regressions on the average yearly time improvements in the 1500 experienced by athletes from each of the Ivies during the period 2013-2018. Only sub 4:00 1500 times were included. Below is the ranking with the linear regression equation including the starting time and the amount of time one could expect to cut each year. Essentially you can plug your year in to find an "average" time at each of these schools. The lower the constant value, the faster the athletes typically run their freshman year, the more negative the second part, the greater the expected improvement.
Entire league average: 1500 time = 232.87-.93(year)
1. Penn 235.66-1.64(year)
2. Cornell 232.74-1.49(year)
3. Yale 232.36-1.23(year)
4. Princeton 231.38-1.22(year)
5. Brown 231.57-1.05(year)
6. Dartmouth 233.30-.58(year)
7. Columbia 231.29-.12(year)
8. Harvard 230.07+1.05(year) lol you can expect to get slower if you are at Harvard
Feel free to discuss the rankings or provide anecdotal evidence.. I may do this for another conference or another event.