I should add that if you’re used to only 3-5min loops then maybe best to only go for about 10-12min.
I only do full 15min after I built up comfortably around 7-8min.
Remember Saint mentioned the subs are built in 4 levels, so my feeling is jumping from level 1 to an occasional peek into level 3 can be fine but all the way to level 4 might not be as fruitful, that’s 3 full levels exposure.
But if I’m used to level 1 and 2 already then the occasional jump to level 4 is fine.
This is all based on personal experience and my own sensitivity to subs.
I get everything I need from these programs and get no negative exposure symptoms as long as I don’t go over 8mins when doing a 3 stack so running 15mins loops is more out of curiosity and not frequent at all.