You've got a valid point here. I've read CTS favors the 3 weeks on a specific skill, then a rest week, then moving on. Maybe that approach would give me better gains.
Only issue is that at my age (57), recovery from repeated hard days isn't as easy as it once was. I've got a lot more time and energy to devote to training now that I'm retired, but the downside is I got rather old somewhere between my '74 Raleigh Gran Sport and my '04 SANO.
Agree the trainer with a power measurement capability is an excellent way to get your repeated constant loads; outdoor hills are rarely that perfect. Still, indoor efforts always seem even tougher to me. 15 x 3 mins on would be a little much, but I could start with 3-5 intervals and work up. Do you hit near max HR on these low-cadence grinds? Assume the first few are fairly easy, then it gets painful in a hurry.