I am a little confused about what looks like conflicting information on cardio. I life three nights a week, and ride a stationary bike beforehand - for between 10 and 25 minutes. One other night I usually swim laps(120 14meter laps, takes a little less than an hour). Another night I do 20 minutes on the stair master/20 on stationary bike (no lifting)

I've seen a lot on here about HIIT - which seems like you alternate beween pushing yourself and dropping back in short intervals. I've also seen that you don't start burning fat until after 15 minutes of cardio.

I weigh 165, and that's 70 some pounds down from where I started four+ years ago. I'd like to lose another 15 pounds, but also continue to improve my lifting strength/endurance. So my questions (sorry, it takes me forever to come to the point) are - am I really getting no fat burning out of the cardio warm-ups unless I go more than 15 minutes? If I tried to switch to HIIT on lifting nights, would that just negatively impact my lifting? And does the 15 minute fat burnng 'rule' not apply to HIIT?

Thanks for advice.

Curious - where did you get this " 15 minute fat burning 'rule' " from ?

Actually you burn fat 24 / 7 - and even during a low intensity warm-up of 15 minutes , you're likely burning more fat than sugars during that time.

Don't you burn sugar and carbs during the first 10-15 minutes?