1.5-2 hour nap?

My 20 month old has been on one nap since around 12.5 months. We’ve had capped nap to 2 hours since maybe 8ish months and it’s been great. Last 3 mornings she’s been waking at 6, instead of 7. No real problems, but wondering if we should try cutting her nap down to 1.5 hours instead? We’ve noticed if she naps less (she’ll wake up herself), her nights are a bit longer but still from a 8 pm bedtime. I just don’t want 6 am to be her new wake up. Thanks!