I also agree the climb to Orisson is steeper - but it is shorter. I used the Gaia GPS hiking app to track both of my Caminos (Frances in 2023, Portuguese in 2024).
Orisson is about 7.5 km /4.6 miles from St. Jean according to the
Wise Pilgrim app; for me Gaia GPS recorded 4.65 miles and an elevation gain for about 2050 feet - but the last two miles was significantly steeper than the previous section.
My walk from Pontevedra to Armenteria was a bit over 14 miles and Gaia GPS recorded an elevation gain of about 1800 feet - less than the shorter trek to Orisson. Again, the second half of that, the last 7 miles, was steeper than the first section.
My point is Orisson will be a steeper walk, especially the last half, but it is not as long.
Be aware that different apps report elevation gain differently, often by significant amounts, so using the same app for two walks provides some comparability, it will not match a different app.
That said, you can make any climb easier by training for elevation gain before you leave. If you do not live near hills or mountains, you can try using a Stair Stepping machine in a gym or elsewhere. It will help, but it's not the same because you are not actually changing elevation and fighting gravity. You will improve your leg strength.
Remember too that Orisson is a much shorter walk than the next day up to the peak then down steeply to Roncessvalles. Train for elevation loss too.
One last point: rest when you feel you need to. No shame.
Buen Camino