Switching to one nap

For those of you who’s baby/toddler were on a 2 nap a day schedule, at what point did they switch to one nap a day? How did you know or decide when it was time?

My daughter has been on a consistent, 2 naps per day schedule for 8 months (same time and length each day). she naps from 11-1 and then again from 4-5. Just trying to get a heads up what to look out for in advance because I feel like her schedule is going to change soon. She will be 15 months this month.

*if your child wasn’t ever taking 2 naps a day, this question doesn’t apply to you😁I mean that in a nice way lol