How do you guys stay put after 15 minutes of reading?

I mean I get that putting in time is important but it's really hard to stay focused for that long. For me, even when it just skips to a new paragraph, I feel like my brain just clears and I have to recollect the last sentence that I read and reconnect what I just read to what I was just reading. That's like 3-4 times a page, which makes even 15 minutes feel like a marathon.